We limit the number of concurrent blob downloads per node and per recovery, but if a user configures too many concurrent recoveries they may run out of per-node download permits which yields the following message:

> Unable to acquire permit to use snapshot files during recovery, this recovery will recover index files from the source node. Ensure snapshot files can be used during recovery by setting [indices.recovery.max_concurrent_snapshot_file_downloads] to be no greater than [25]

The `[25]` here is wrong, the 25 permits are shared across all inbound recoveries so we should divide the suggested value by `cluster.routing.allocation.node_concurrent_incoming_recoveries`. In extreme cases the user may have configured so many concurrent recoveries that the only reasonable limit is zero, and in that case we should suggest setting `indices.recovery.use_snapshots: false` instead.


server/src/main/java/org/elasticsearch/indices/recovery/RecoverySettings.java
this.maxBytesPerSec = maxBytesPerSec;
        if (maxBytesPerSec.getBytes() <= 0) {
            rateLimiter = null;
        } else if (rateLimiter != null) {
            rateLimiter.setMBPerSec(maxBytesPerSec.getMbFrac());
        } else {
            rateLimiter = new SimpleRateLimiter(maxBytesPerSec.getMbFrac());
        }
    }
    public ByteSizeValue getMaxBytesPerSec() {
        return maxBytesPerSec;
    }
    public int getMaxConcurrentFileChunks() {
        return maxConcurrentFileChunks;
    }
    private void setMaxConcurrentFileChunks(int maxConcurrentFileChunks) {
        this.maxConcurrentFileChunks = maxConcurrentFileChunks;
    }
    public int getMaxConcurrentOperations() {
        return maxConcurrentOperations;
    }
    private void setMaxConcurrentOperations(int maxConcurrentOperations) {
        this.maxConcurrentOperations = maxConcurrentOperations;
    }
    public boolean nodeBandwidthSettingsExist() {
        return nodeBandwidthSettingsExist;
    }
    public boolean getUseSnapshotsDuringRecovery() {
        return useSnapshotsDuringRecovery;
    }