iptables: Skip CILIUM_TRANSIENT_FORWARD for IPv6
iptables: Skip CILIUM_TRANSIENT_FORWARD for IPv6

Commit 317a671 ("iptables: Populate CILIUM_FORWARD chain for IPv6")
fixed the agent to add IPv6 counterparts to the Cilium IPv4 rules in
CILIUM_FORWARD. The same method is however used to install rules in
CILIUM_FORWARD and CILIUM_TRANSIENT_FORWARD. The IPv6 chain for
CILIUM_TRANSIENT_FORWARD doesn't exist, resulting in the following
error message:

    level=error msg="Command execution failed" cmd="[ip6tables -w 5 -A CILIUM_TRANSIENT_FORWARD -o cilium_host -m comment --comment cilium (transient): any->cluster on cilium_host forward accept -j ACCEPT]" error="exit status 1" subsys=iptables
    level=warning msg="ip6tables: No chain/target/match by that name." subsys=iptables
    level=warning msg="failed to install transient iptables rules" error="cannot install forward chain rules to CILIUM_TRANSIENT_FORWARD: exit status 1" subsys=datapath-loader

This commit fixes it by skipping the installation of IPv6 rules in
CILIUM_TRANSIENT_FORWARD. If we want those rules, more work is required.

Fixes: 317a671 ("iptables: Populate CILIUM_FORWARD chain for IPv6")
Signed-off-by: Paul Chaignon <a027184a55211cd23e3f3094f1fdc728df5e0500@cilium.io>

michi-covalent/cilium,tklauser/cilium,tgraf/cilium,cilium/cilium,tklauser/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,tgraf/cilium,tklauser/cilium,michi-covalent/cilium,michi-covalent/cilium,cilium/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,michi-covalent/cilium