platform: fix compile error in event_seq_check()

Some compiler versions don't like this. Workaround.

  src/libnm-platform/nm-linux-platform.c: In function event_seq_check:
  src/libnm-platform/nm-linux-platform.c:7254:1: error: label at end of compound statement
   out:
   ^~~

Fixes: 3d4906a3da ('platform: add genl socket support for events and genl family')

src/libnm-platform/nm-linux-platform.c

@@ -7257,6 +7257,8 @@ out:
     if (seq_number != priv->proto_data_x[netlink_protocol].nlh_seq_last_handled)
         _LOGt("netlink: recvmsg: unwaited sequence number %u", seq_number);
     priv->proto_data_x[netlink_protocol].nlh_seq_last_handled = seq_number;
+#else
+    (void) 0;
 #endif
 }