Fix clearing MAC stats registers. Previously it cleared every
fourth register.

Submitted by:	Paul A. Patience <paul-a.patience@polymtl.ca>
Approved by:	re (gjb)
Add epair(4) support in $cloned_interfaces.  One should be specified
as "epair0" in $cloned_interfaces and "epair0[ab]" in the others in
rc.conf like the following:

 cloned_interfaces="epair0"
 ifconfig_epair0a="inet 192.168.1.1/24"
 ifconfig_epair0b="inet 192.168.2.1/24"

/etc/rc.d/netif now accepts both "netif start epair0" and "netif start
epair0a".

Approved by:	re (kib)