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>