zebra: make if_subnet_delete a bit more strict

Enhance if_subnet_delete so it will complain about improper use.
Also, fix one occurence of improper use where it was called for
IPv6 as well.

Signed-off-by: Christian Franke <chris@opensourcerouting.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
2 files changed