io_uring/net: save msg_control for compat

Match the compat part of io_sendmsg_copy_hdr() with its counterpart and
save msg_control.

Fixes: c559780 ("io_uring/net: move receive multishot out of the generic msghdr path")
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/2a8418821fe83d3b64350ad2b3c0303e9b732bbd.1740498502.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: isilence

io_uring/net.c

@@ -322,7 +322,9 @@ static int io_sendmsg_copy_hdr(struct io_kiocb *req,
 		if (unlikely(ret))
 			return ret;
 
-		return __get_compat_msghdr(&iomsg->msg, &cmsg, NULL);
+		ret = __get_compat_msghdr(&iomsg->msg, &cmsg, NULL);
+		sr->msg_control = iomsg->msg.msg_control_user;
+		return ret;
 	}
 #endif