VLAN aux info for AF_PACKET available only with ETH_P_ALL

["Peter Palúch" <Peter.Paluch@fri.uniza.sk>]

Greetings,

I am running vanilla Linux kernel v4.4.6.

When using AF_PACKET sockets with PACKET_AUXDATA socket option to access 
the VLAN TCI information of received frames, I have noticed that the 
VLAN information in struct tpacket_auxdata, namely,

- tp_vlan_tci
- tp_vlan_tpid
- TP_STATUS_VLAN_VALID and TP_STATUS_VLAN_TPID_VALID flags

is filled in only when the socket is bound to htons (ETH_P_ALL). If the 
socket is bound to any specific protocol, the VLAN information fields in 
struct tpacket_auxdata are set to 0 even if the datagram of the specific 
protocol was received in an 802.1Q-tagged frame.

Is this behavior intentional? If not, I would be honored to try to 
provide a patch but I am not well-versed in kernel internals so any 
guidance would be most appreciated.

Thanks!

Best regards,
Peter