dnmasq.init now invokes ipcalc.sh as either:
ipcalc.sh address/netmask ...
or:
ipcalc.sh address/prefix
but the existing version doesn't accept the 2nd notation. We're
trying to rationalize the usage of ipcalc.sh, and here we add
support for the 2nd format.
Signed-off-by: Philip Prindeville <philipp@redfish-solutions.com>