xdp: Add VLAN tag hint

Implement functionality that enables drivers to expose VLAN tag
to XDP code.

VLAN tag is represented by 2 variables:
- protocol ID, which is passed to bpf code in BE
- VLAN TCI, in host byte order

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Link: https://lore.kernel.org/r/20231205210847.28460-10-larysa.zaremba@intel.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>