Make specification of NETMASK and GATEWAY mandatory; they cannot be

Make specification of NETMASK and GATEWAY mandatory; they cannot be
assumed to have global values that are valid for all NICs.  This update
is largely to keep up appearances, as this package is no longer used.
But, since it is still installed, and we need to get rid of the
network section in master.yaml (which this package is the only consumer
of), here we are.