batadv: Slight optimization of batadv_compare_eth

Use the newly added generic routine ether_addr_equal_unaligned
to test if possibly unaligned to u16 Ethernet addresses are equal.

This slightly improves comparison time for systems with
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>