Routes with a non-zero host part are not allowed by kernel and
don't really exist. We didn't reject such routes in users configuration,
so various part of NM allow such routes. NM should silently strip
the host part.

Extend the cache's route ID to clear the host part too.

Note that NM's handling of routes is fundamentally flawed, as
for kernels routes don't have an "id" (or rather: all properties
of a route are part of it's ID, not only the family,ifindex,
network/plen and metric tuple (see related bug rh#1337855).