io_uring: delay req queueing into compl-batch list

io_req_complete_state() is inlined and used in lots of places, so we
want to keep it concise. Move adding a request into a completion batch
list from io_req_complete_state() into the consumer, i.e.
__io_queue_sqe().

before vs after
   text    data     bss     dec     hex filename
  91894   14002       8  105904   19db0 ./fs/io_uring.o
  91046   14002       8  105056   19a60 ./fs/io_uring.o

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/4afca4e11abfd4cc8e99777fdcaf4d34cf4d022d.1633373302.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>