py: parse ISD-AS from integer
py: parse ISD-AS from integer

GitOrigin-RevId: ace3b93e2df5738990ae379dbc8081e0c2c1ce9b

Oncilla/scion,netsec-ethz/scion,Oncilla/scion,netsec-ethz/scion,Oncilla/scion,Oncilla/scion,netsec-ethz/scion,netsec-ethz/scion