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/test/java/org/elasticsearch/indices/recovery/RecoverySettingsTests.java
}
        RecoverySettings build() {
            final Settings.Builder settings = Settings.builder();
            settings.put(TOTAL_PHYSICAL_MEMORY_OVERRIDING_TEST_SETTING.getKey(), Objects.requireNonNull(physicalMemory));
            if (roles.isEmpty() == false) {
                settings.putList(NODE_ROLES_SETTING.getKey(), new ArrayList<>(roles));
            }
            if (indicesRecoveryMaxBytesPerSec != null) {
                settings.put(INDICES_RECOVERY_MAX_BYTES_PER_SEC_SETTING.getKey(), indicesRecoveryMaxBytesPerSec);
            }
            if (networkBandwidth != null) {
                settings.put(NODE_BANDWIDTH_RECOVERY_NETWORK_SETTING.getKey(), networkBandwidth);
            }
            if (diskReadBandwidth != null) {
                settings.put(NODE_BANDWIDTH_RECOVERY_DISK_READ_SETTING.getKey(), diskReadBandwidth);
            }
            if (diskWriteBandwidth != null) {
                settings.put(NODE_BANDWIDTH_RECOVERY_DISK_WRITE_SETTING.getKey(), diskWriteBandwidth);
            }
            if (operatorDefaultFactor != null) {
                settings.put(NODE_BANDWIDTH_RECOVERY_OPERATOR_FACTOR_SETTING.getKey(), operatorDefaultFactor);
            }
            if (maxOvercommitFactor != null) {
                settings.put(NODE_BANDWIDTH_RECOVERY_OPERATOR_FACTOR_MAX_OVERCOMMIT_SETTING.getKey(), maxOvercommitFactor);
            }
            return new RecoverySettings(settings.build(), new ClusterSettings(Settings.EMPTY, ClusterSettings.BUILT_IN_CLUSTER_SETTINGS));
        }
    }
}