[BUGFIX] cmpIPv4: prevent E_NOTICE, cleanup compare, testcases

Cleanup for an E_NOTICE on exploding the bitmask.
Replaced (correct working, but "unreadable") strcmp().
Add testcases.

Change-Id: I3836d3c53ab6093e3427047c4a5089778dd04ca2
Resolves: #27230
Releases: 4.3, 4.4, 4.5, 4.6
Reviewed-on: http://review.typo3.org/2536
Reviewed-by: Björn Pedersen
Tested-by: Björn Pedersen
Reviewed-by: Andreas Wolf
Tested-by: Andreas Wolf