Decode and validate ASPA objects following the v1 syntax

Decode and validate ASPA objects following the v1 syntax

Through draft-ietf-sidrops-aspa-profile-15, the ASPA profile was
made AFI-agnostic. This represents a simplification for both operators
and implementers in both the RPKI and BGP layers of the stack.

This update changes the JSON structure.

No effort was made to simultaneously support ASPA v0 and v1 objects.

OK tb@ claudio@