Separate the two checks for single vlan and multiple vlans in
netif_skb_features().  This allows us to move the check for multiple
vlans to another function later.
Signed-off-by: NToshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>