[PKTGEN]: Replacing with (compare|is_zero)_ether_addr() and ETH_ALEN

This replaces some tests with is_zero_ether_addr(), memcmp(one, two,
6) with compare_ether_addr(one, two), and 6 with ETH_ALEN where
appropriate.

Signed-off-by: Kris Katterjohn <kjak@users.sourceforge.net>
Signed-off-by: David S. Miller <davem@davemloft.net>