net: plip: slight optimization of addr compare

Use possibly more efficient ether_addr_equal_64bits
to instead of memcmp.

Cc: "David S. Miller" <davem@davemloft.net>
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>