Wire up the libnl utilities Jeff and Ralph added previously to
the netlink reachable component so that it actually does work.
The algorithm is a bit simplistic, but should work for our use
cases. If there's a route, assume the two interfaces can talk.
If there's no gateway, assume the two interfaces are in the
same subnet, and give preference to that connection. If there's
a gateway, assume there's a route, but the interfaces are not
in the same subnet.
Signed-off-by: Brian Barrett <bbarrett@amazon.com>