io_uring/zcrx: grab a net device

io_uring/zcrx: grab a net device

Zerocopy receive needs a net device to bind to its rx queue and dma map
buffers. As a preparation to following patches, resolve a net device
from the if_idx parameter with no functional changes otherwise.

Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David Wei <dw@davidwei.uk>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20250215000947.789731-4-dw@davidwei.uk
Signed-off-by: Jens Axboe <axboe@kernel.dk>