io_uring/net: don't clear REQ_F_NEED_CLEANUP unconditionally

io_req_msg_cleanup() relies on the fact that io_netmsg_recycle() will
always fully recycle, but that may not be the case if the msg cache
was already full. To ensure that normal cleanup always gets run,
let io_netmsg_recycle() deal with clearing the relevant cleanup flags,
as it knows exactly when that should be done.

Cc: stable@vger.kernel.org
Reported-by: David Wei <dw@davidwei.uk>
Fixes: 75191341 ("io_uring/net: add iovec recycling")
Signed-off-by: Jens Axboe <axboe@kernel.dk>