MB-30610: Don't fail server_socket() if at least one protocol successful
MB-30610: Don't fail server_socket() if at least one protocol successful

When attempting to listen to all protocols on a given network
interface, return success from server_socket() as long as at least one
of IPv4,IPv6 was successful.

Note this restores to the pre-5.5 behaviour -
http://review.couchbase.org/#/c/90791/ (added in 5.5) changed to fail
if any protocol which was enabled failed.

Change-Id: I6533b9d53459542778d75844d60883fa37f03aec
Reviewed-on: http://review.couchbase.org/97325
Reviewed-by: Trond Norbye <60edd2ef23891a753f231b0c6f161dc634079a93@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine