Added functionality for checking network (w/o netmask)

- Added mostly for IPv6 support bnc#800592
Using new IP::CheckNetwork functionality in Firewall
Fixed modified function to return something

- This is NOT Ruby!
Fixed wrong testcase
Added changes file entries (12.3)
New version for maitenance 2.23.23.1
Merge pull request #76 from kobliha/openSUSE-12_3

Bugfix for BNC#800592