interfaces: null route for delegated prefix #3304
interfaces: null route for delegated prefix #3304

It's still debatable if ifctl is a tool to record data
for interfaces and act on it or if the latter part should
be handled by more authorative (interface) code.

Inspired by: https://github.com/opnsense/core/pull/5992

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core