netfilter: Update ip6_route_me_harder to consider L3 domain

netfilter: Update ip6_route_me_harder to consider L3 domain

BugLink: https://bugs.launchpad.net/bugs/1978234
commit 8ddffdb9442a9d60b4a6e679ac48d7d21403a674 upstream.

The commit referenced below fixed packet re-routing if Netfilter mangles
a routing key property of a packet and the packet is routed in a VRF L3
domain. The fix, however, addressed IPv4 re-routing, only.

This commit applies the same behavior for IPv6. While at it, untangle
the nested ternary operator to make the code more readable.

Fixes: 6d8b49c3a3a3 ("netfilter: Update ip_route_me_harder to consider L3 domain")
Cc: stable@vger.kernel.org
Signed-off-by: Martin Willi <martin@strongswan.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>