Always create a local route for every configured IPv4 address on the

Always create a local route for every configured IPv4 address on the
machine and restore the original behavior of RTM_ADD and RTM_DELETE
by always generating one message per locally configured address.

This time, make sure the local route is removed during an address change,
since at least pppoe(4) do some funky magics with wildcard addresses that
might corrupt the routing tree, as found by naddy@

Also do not add a local route if the specified address is 0.0.0.0, to
prevent a tree corruption, as found by guenther@.

Putting this in now so that it gets tested, claudio@ agrees.  Please
contact me if you find any route-related regression caused by this
change.