Make posix tcp client add itself to interested parties when needed

src/core/iomgr/tcp_client_posix.c

@@ -235,6 +235,8 @@ void grpc_tcp_client_connect(void (*cb)(void *arg, grpc_endpoint *ep),
   ac->write_closure.cb = on_writable;
   ac->write_closure.cb_arg = ac;
 
+  grpc_pollset_set_add_fd(interested_parties, ac->fd);
+
   grpc_alarm_init(&ac->alarm, deadline, on_alarm, ac, gpr_now());
   grpc_fd_notify_on_write(ac->fd, &ac->write_closure);
 }