netfilter: nftables_offload: VLAN id needs host byteorder in flow dissector

The flow dissector representation expects the VLAN id in host byteorder.
Add the NFT_OFFLOAD_F_NETWORK2HOST flag to swap the bytes from nft_cmp.

Fixes: a82055af

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