Ensure BIRD6 can make correct routing decisions.
Ensure BIRD6 can make correct routing decisions.

This is the same fix as 08c0741 for BIRD6. Weirdly, BIRD6 was missing
default route filters. This didn't seem to cause a problem in the systems
we've used, but it looks odd so I added a safety check for it anyway.

matthewdupre/felix,neiljerram/felix,fasaxc/felix,kasisnu/calico,matthewdupre/felix,TrimBiggs/calico,alexaltair/calico,fasaxc/felix,anortef/calico,ocadotechnology/calico,neiljerram/felix,nbartos/calico,kasisnu/calico,alexhersh/calico,anortef/calico,alexaltair/calico,Metaswitch/calico,nbartos/calico,neiljerram/felix,TrimBiggs/calico,beddari/calico,ocadotechnology/calico,neiljerram/felix,beddari/calico,alexhersh/calico,Metaswitch/calico