perl: revert "remove one more unreliable test, fixes #454"

Commit 70f0d79d063c665a9fd46d5bd38391f940f0430f causes a massive rebuild
that I'd like to avoid until my GCC 4.8.x switch is done.
guile: don't run IPv6 related tests if the build machine doesn't support them

Patch supplied by Ludo!