Client behavior for ASPA AS0 and Prefix PDUs

[randomthingsandstuff]

Is AS0 handling & zeroizing host bits sorted out though? The next version of 8210bis will have some extra canonicalization rules to avoid payload malleability:

• An ASPA announcement PDU containing multiple Provider Autonomous System Numbers MUST NOT contain AS 0 or an Error PDU with code 9 is returned.
• Strictly speaking, the only data that a router client needs from the Prefix PDU is that indicated by the Prefix Length. For example, if the Prefix Length is eight, then only the first eight bits of the Prefix are required for a router client to make use of the PDU. Notwithstanding this, the cache server MUST set the remaining bits of the Prefix to zero, for consistency with the approach used for the other unused components of the PDU.

Since StayRTR is both server & client it is important to ensure these checks are present

Originally posted by @job in #156 (comment)