netfilter: nft_payload: restore vlan q-in-q match support

Revert f6ae9f12 ("netfilter: nft_payload: add C-VLAN support").

f41f72d0 ("netfilter: nft_payload: simplify vlan header handling")
already allows to match on inner vlan tags by subtract the vlan header
size to the payload offset which has been popped and stored in skbuff
metadata fields.

Fixes: f6ae9f12

 ("netfilter: nft_payload: add C-VLAN support")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>