Add rules to route IPv6 third party VPN traffic

Currently only IPv4 traffic is handled by third party VPNs.  Extend
the UID_MATCH and route setup to IPv6.

Bug: chromium:522003
TEST=`FEATURES=test emerge-link firewalld`
TEST=manual

Change-Id: I9352506e98e1fdcace093d443e2fa2b95887d720
4 files changed