io_uring/cmd: kill one issue_flags to tw conversion

io_uring cmd converts struct io_tw_state to issue_flags and later back
to io_tw_state, it's awfully ill-fated, not to mention that intermediate
issue_flags state is not correct.

Get rid of the last conversion, drag through tw everything that came
with IO_URING_F_UNLOCKED, and replace io_req_complete_defer() with a
direct call to io_req_complete_defer(), at least for the time being.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/c53fa3df749752bd058cf6f824a90704822d6bcc.1710799188.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>