Add aspa-set to openbgpd config output.

Add aspa-set to openbgpd config output.

Change the way the validated ASPA tree is built since OpenBGPD config
follows more the ASPA profile and puts the optional AFI to each provider
ASnum instead of duplicated everything into an IPv4 and IPv6 tree.
The JSON output of ASPA is still the same.

The inclusion of the aspa-set can currently be disabled by the -A flag.
OK tb@