net: flow_dissector: add 802.1ad support

Same behavior than 802.1q : finds the encapsulated protocol and
skip 32bit header.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -65,6 +65,7 @@ ipv6:
 		nhoff += sizeof(struct ipv6hdr);
 		break;
 	}
+	case __constant_htons(ETH_P_8021AD):
 	case __constant_htons(ETH_P_8021Q): {
 		const struct vlan_hdr *vlan;
 		struct vlan_hdr _vlan;