macvlan: Remove custom recieve and forward handlers

Since now macvlan and macvtap use the same receive and
forward handlers, we can remove them completely and use
netif_rx and dev_forward_skb() directly.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>