net: vlan: add protocol argument to packet tagging functions

Add a protocol argument to the VLAN packet tagging functions. In case of HW
tagging, we need that protocol available in the ndo_start_xmit functions,
so it is stored in a new field in the skb. The new field fits into a hole
(on 64 bit) and doesn't increase the sks's size.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>