In 8.3 the default TCP keep alive settings introduced in https://github.com/elastic/elasticsearch/pull/59278 are not applied by default, therefore it uses the OS default values. See:

8.3.0:
```
cat connections-8.3.0.txt  | grep -e '930[01]' | head
ESTAB  0       0         [::ffff:127.0.0.1]:46818     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837419 sk:a2 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37928     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834869 sk:a3 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46808   timer:(keepalive,119min,0) uid:1038 ino:6830957 sk:a4 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37942     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834871 sk:a5 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46828   timer:(keepalive,119min,0) uid:1038 ino:6834882 sk:a6 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37926     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834868 sk:a7 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46826   timer:(keepalive,119min,0) uid:1038 ino:6834881 sk:a8 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46824     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837425 sk:a9 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37944     [::ffff:127.0.0.1]:9300    timer:(keepalive,119min,0) uid:1038 ino:6834879 sk:aa <->
ESTAB  0       0         [::ffff:127.0.0.1]:46828     [::ffff:127.0.0.1]:9301    timer:(keepalive,119min,0) uid:1038 ino:6837430 sk:ab <->
```

8.2.2:
```
cat connections-8.2.2.txt  | grep -e '930[01]' | head
ESTAB  0       0         [::ffff:127.0.0.1]:46752     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833637 sk:6e <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46746   timer:(keepalive,4min52sec,0) uid:1038 ino:6831684 sk:6f <->
ESTAB  0       0         [::ffff:127.0.0.1]:46732     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833629 sk:70 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37876     [::ffff:127.0.0.1]:9300    timer:(keepalive,4min52sec,0) uid:1038 ino:6833618 sk:71 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46730   timer:(keepalive,4min52sec,0) uid:1038 ino:6831676 sk:72 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46748     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833640 sk:73 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46736     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833631 sk:74 <->
ESTAB  0       0         [::ffff:127.0.0.1]:9301      [::ffff:127.0.0.1]:46732   timer:(keepalive,4min52sec,0) uid:1038 ino:6831677 sk:75 <->
ESTAB  0       0         [::ffff:127.0.0.1]:37860     [::ffff:127.0.0.1]:9300    timer:(keepalive,4min52sec,0) uid:1038 ino:6833611 sk:76 <->
ESTAB  0       0         [::ffff:127.0.0.1]:46734     [::ffff:127.0.0.1]:9301    timer:(keepalive,4min52sec,0) uid:1038 ino:6833630 sk:77 <->
```

It's possible that after moving `NetUtil` to the netty module https://github.com/elastic/elasticsearch/pull/85953 some of the internal details used are not available anymore.
modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpServerTransport.java
private static final ByteSizeValue MTU = new ByteSizeValue(Long.parseLong(System.getProperty("es.net.mtu", "1500")));
    private static final String SETTING_KEY_HTTP_NETTY_MAX_COMPOSITE_BUFFER_COMPONENTS = "http.netty.max_composite_buffer_components";
    public static Setting<Integer> SETTING_HTTP_NETTY_MAX_COMPOSITE_BUFFER_COMPONENTS = new Setting<>(
        SETTING_KEY_HTTP_NETTY_MAX_COMPOSITE_BUFFER_COMPONENTS,
        (s) -> {
            ByteSizeValue maxContentLength = SETTING_HTTP_MAX_CONTENT_LENGTH.get(s);
            /*
             * Netty accumulates buffers containing data from all incoming network packets that make up one HTTP request in an instance of
             * io.netty.buffer.CompositeByteBuf (think of it as a buffer of buffers). Once its capacity is reached, the buffer will iterate
             * over its individual entries and put them into larger buffers (see io.netty.buffer.CompositeByteBuf#consolidateIfNeeded()
             * for implementation details). We want to to resize that buffer because this leads to additional garbage on the heap and also
             * increases the application's native memory footprint (as direct byte buffers hold their contents off-heap).
             *
             * With this setting we control the CompositeByteBuf's capacity (which is by default 1024, see
             * io.netty.handler.codec.MessageAggregator#DEFAULT_MAX_COMPOSITEBUFFER_COMPONENTS). To determine a proper default capacity for
             * that buffer, we need to consider that the upper bound for the size of HTTP requests is determined by `maxContentLength`. The
             * number of buffers that are needed depend on how often Netty reads network packets which depends on the network type (MTU).
             * We assume here that Elasticsearch receives HTTP requests via an Ethernet connection which has a MTU of 1500 bytes.
             *
             * Note that we are *not* pre-allocating any memory based on this setting but rather determine the CompositeByteBuf's capacity.
             * The tradeoff is between less (but larger) buffers that are contained in the CompositeByteBuf and more (but smaller) buffers.
             * With the default max content length of 100MB and a MTU of 1500 bytes we would allow 69905 entries.
             */
            long maxBufferComponentsEstimate = Math.round((double) (maxContentLength.getBytes() / MTU.getBytes()));
            
            long maxBufferComponents = Math.max(2, Math.min(maxBufferComponentsEstimate, Integer.MAX_VALUE));
            return String.valueOf(maxBufferComponents);
            
        },
        s -> Setting.parseInt(s, 2, Integer.MAX_VALUE, SETTING_KEY_HTTP_NETTY_MAX_COMPOSITE_BUFFER_COMPONENTS),