Return bound port number from grpc_server_add_http2_port.

Allows tests to bind to port 0 and still have clients connect to them.
	Change on 2015/01/12 by ctiller <ctiller@google.com>
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=83800669
diff --git a/include/grpc/grpc.h b/include/grpc/grpc.h
index 323a944..0853930 100644
--- a/include/grpc/grpc.h
+++ b/include/grpc/grpc.h
@@ -428,7 +428,8 @@
 grpc_server *grpc_server_create(grpc_completion_queue *cq,
                                 const grpc_channel_args *args);
 
-/* Add a http2 over tcp listener; returns 1 on success, 0 on failure
+/* Add a http2 over tcp listener.
+   Returns bound port number on success, 0 on failure.
    REQUIRES: server not started */
 int grpc_server_add_http2_port(grpc_server *server, const char *addr);