remote: limit number of open tcp connections by default. Fixes #5491

This change limits the number of open tcp connections
by default to 100 for remote caching. We have had error
reports where some use cases Bazel would open so many
TCP connections that it crashed/ran out of sockets. The
max. number of TCP connections can still be adjusted by
specifying --remote_max_connections.

See also #5047.

RELNOTES: In remote caching we limit the number of open
TCP connections to 100 by default. The number can be adjusted
by specifying the --remote_max_connections flag.
PiperOrigin-RevId: 202958838

Author: buchgr

src/main/java/com/google/devtools/build/lib/remote/RemoteOptions.java

@@ -37,12 +37,13 @@ public final class RemoteOptions extends OptionsBase {
 
   @Option(
       name = "remote_max_connections",
-      defaultValue = "0",
+      defaultValue = "100",
       documentationCategory = OptionDocumentationCategory.UNCATEGORIZED,
       effectTags = {OptionEffectTag.HOST_MACHINE_RESOURCE_OPTIMIZATIONS},
       help =
           "The max. number of concurrent network connections to the remote cache/executor. By "
-              + "default Bazel selects the ideal number of connections automatically.")
+              + "default Bazel limits the number of TCP connections to 100. Setting this flag to "
+              + "0 will make Bazel choose the number of connections automatically.")
   public int remoteMaxConnections;
 
   @Option(