Currently force_nonblock stands for three meanings:
 - nowait or not
 - in an io-worker or not(hold uring_lock or not)

Let's split the logic to two flags, IO_URING_F_NONBLOCK and
IO_URING_F_UNLOCKED for convenience of the next patch.
Suggested-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NHao Xu <haoxu@linux.alibaba.com>
Reviewed-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/20211018133431.103298-1-haoxu@linux.alibaba.comSigned-off-by: NJens Axboe <axboe@kernel.dk>