Remove per-AFI ASPA handling in bgpd internals

Remove per-AFI ASPA handling in bgpd internals

With draft-ietf-sidrops-aspa-profile-16 and
draft-ietf-sidrops-aspa-verification-15 the AFI dependence of ASPA
records was dropped. So remove this complication form the code.

This only removes the AFI handling internally in bgpd but still allows
the old syntax in aspa-set tables. The optional address family is just
ignored and records are merged together.

For RTR sessions draft-ietf-sidrops-8210bis has not yet been updated so
right now we still handle RTR sessions as specified there. The IPv4 and
IPv6 ASPA entries are handled in two trees and merged together into one
AFI independent tree. This is the best we can do for now until IETF
updates draft-ietf-sidrops-8210bis.

OK tb@ job@