Claim IPv6 is unsupported if no interface with IPv6 configured

When IPv6 is supported by glibc but no interface
is configured to use ipv6 (because the ipv6 module
is not loaded), skip ipv6 related checks.

Change-Id: I15aaf3d01f0f51bdc0bd29f30728ca2ab8b5c30a
Merge "Claim IPv6 is unsupported if no interface with IPv6 configured"