io_uring/net: move charging socket out of zc io_uring

io_uring/net: move charging socket out of zc io_uring

Currently, io_uring's io_sg_from_iter() duplicates the part of
__zerocopy_sg_from_iter() charging pages to the socket. It'd be too easy
to miss while changing it in net/, the chunk is not the most
straightforward for outside users and full of internal implementation
details. io_uring is not a good place to keep it, deduplicate it by
moving out of the callback into __zerocopy_sg_from_iter().

Signed-off-by: Pavel Begunkov <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
Reviewed-by: Jens Axboe <[email protected]>
Signed-off-by: Paolo Abeni <[email protected]>