hyperv: Fix vlan_proto setting in netvsc_recv_callback()

Since the recent addition of 8021AD, we need to set the new field vlan_proto in
sk_buff. Otherwise, it will trigger BUG() call in vlan_proto_idx().

This patch fixes the problem.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>