io_uring/query: return support for custom rx page size

io_uring/query: return support for custom rx page size

Add an ability to query if the zcrx rx page size setting is available.

Note, even when the API is supported by io_uring, the registration can
still get rejected for various reasons, e.g. when the NIC or the driver
doesn't support it, when the particular specified size is unsupported,
when the memory area doesn't satisfy all requirements, etc.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>