io_uring: inline hot path of __io_queue_sqe()

io_uring: inline hot path of __io_queue_sqe()

Extract slow paths from __io_queue_sqe() into a function and inline the
hot path. With that we have everything completely inlined on the
submission path up until io_issue_sqe().

-> io_submit_sqes()
  -> io_submit_sqe() (inlined)
    -> io_queue_sqe() (inlined)
       -> __io_queue_sqe() (inlined)
         -> io_issue_sqe()

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/f1606864d95d7f26dc28c7eec3dc6ed6ec32618a.1632516769.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>