io_uring/zcrx: add support for multiple ifqs

Allow the user to register multiple ifqs / zcrx contexts. With that we
can use multiple interfaces / interface queues in a single io_uring
instance.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/668b03bee03b5216564482edcfefbc2ee337dd30.1745141261.git.asml.silence@gmail.com


[axboe: fold in fix]
Signed-off-by: Jens Axboe <axboe@kernel.dk>