update ifconfig.sh

update ifconfig.sh

* make it harder to get the interface numbers wrong by using 'max'
to specify the upper bound of the sequence of interfaces and use 'max'
when calculating the interface number
* extract the platform specific instruction into 'up' and 'down'
and call them from the inner loop so that the interface number is
calculated in one place.
* calculate the A and AAAA address in a single place rather than
in each command
* use /sbin/ipadm on Solaris 2.11 and greater