* Add multiple routes support in NetworkManager
Support multiple routes to the same network learned via Router
Information Option. With this change, the kernel will have multiple
routing table entries to a given Thread network. The routes gateway
won't be updated with every new RIO any longer since every gateway
has its own entry.
* Enable IPv6 router reachability probing
Currently router reachability probing is disabled since HAOS enables
IPv6 forwarding and the necessary kernel options are not enabled. With
this change router reachability probing is enabled even though we are
a router on our own.
Note that Linux commit ea659e077528 ("[IPV6] ROUTE: Do not enable router
reachability probing in router mode.") by default disabled this
behavior. But since we are acting as a router as well as a host device,
we rather want this reachability probing.
See also: https://lore.kernel.org/netdev/b9182b02829b158d55acc53a0bcec1ed667b2668.1680000784.git.stefan@agner.ch/T/#u
