io_uring/net: rename io_sendzc()

Simple renaming of io_sendzc*() functions in preparatio to adding
a zerocopy sendmsg variant.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/265af46829e6076dd220011b1858dc3151969226.1663668091.git.asml.silence@gmail.com


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