macvlan: Use compare_ether_addr_64bits()

To speedup ether addresses compares, we can use compare_ether_addr_64bits()
(all operands are guaranteed to be at least 8 bytes long)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>