This fixes rtentry leak for the cloned interfaces created inside the
Reported by: rashey at superbox.pl
MFC after: 3 days
Current code cleans up protocol state in ip_destroy(). It includes flushing route entries on a per-interface basis using rt_flushifroutes_af(). The latter function removes all interface routes except ones with RTF_PINNED flag (e.g. interface routes).
As a result, some of the rtentries may leak.
Add rib_flush_routes_af() which removes all of the routes for the specified family in a light-weight fashion and switch IPv4/IPv6 stack teardown to use it instead of iterating over all interfaces with rt_flushroutes_af().