process: add _has_ipv6() function

Add _has_ipv6() function and use it in _configure_loopback_interface()
to decide whether to add an IPv6 address.

Bug: https://bugs.gentoo.org/691290
Reviewed-by: Mike Gilbert <floppym@gentoo.org>
Signed-off-by: Zac Medico <zmedico@gentoo.org>
1 file changed