rds: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break statements instead of
letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Reviewed-by: Håkon Bugge <[e-mail]>
Signed-off-by: Gustavo A. R. Silva <[e-mail]>

net/rds/tcp_connect.c

···
 	case TCP_CLOSE_WAIT:
 	case TCP_CLOSE:
 		rds_conn_path_drop(cp, false);
+		break;
 	default:
 		break;
 	}

net/rds/threads.c

···
 		case -ENOMEM:
 			rds_stats_inc(s_send_delayed_retry);
 			queue_delayed_work(rds_wq, &cp->cp_send_w, 2);
+			break;
 		default:
 			break;
 		}
···
 		case -ENOMEM:
 			rds_stats_inc(s_recv_delayed_retry);
 			queue_delayed_work(rds_wq, &cp->cp_recv_w, 2);
+			break;
 		default:
 			break;
 		}