Missing Bindings for `LWTUNNEL_ENCAP_IP6`

[Toorero]

Currently, this crate is missing abstractions for lwtunnel_ip6_t.

They would need to be added as a new enum type in netlink_packet_route::route::RouteLwTunnelEncap.

[cathay4t]

For anyone(most likely myself) working on this, this command can be used to create route with encap ip6:

sudo ip route add 192.0.2.158/32 \
    encap ip6 id 100 dst 2001:db8:1::1 src 2001:db8:1::2 \
    tc 7 hoplimit 253  dev eth1

[Toorero]

Yes, I should have probably mentioned this, sorry.

My plan was to open this issue to probe if I missed something and later implement it when I find the time to do so.