Static: Allow to define both nexthop and interface

Static: Allow to define both nexthop and interface

Allow to define both nexthop and interface using iproute2-like syntax,
e.g.: route 10.0.0.0/16 via 10.1.0.1 dev "eth0";

Now we can avoid to use link-local scope hack (e.g. 10.1.0.1%eth0)
for cases where both nexthop and interface have to be defined.

Thanks to Marcin Saklak for the suggestion.