net-firewall/shorewall: Always check if we need to (re-)compile the firewall script

Behavior synchronized with upstream's /usr/sbin/shorewall-init
net-firewall/shorewall: Update runscripts to reflect changes from fa01c29c

In fa01c29c73e5d40a93289fdd0cb325c5060bc56d, executables where moved from
/sbin to /usr/sbin. So we need to update the runscripts/service files.