checkpatch: prefer ether_addr_copy to memcpy(foo, bar, ETH_ALEN)

ether_addr_copy was added for kernel version 3.14.  It's slightly
smaller/faster for some arches.  Encourage its use.

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>