QAD on Multipath: do we send all OBSERVED_ADDRESS frames for all paths

[flub]

Looking at the code to send a PATH_CHALLENGE it always includes an OBSERVED_ADDRESS frame. But only for the address observed for that specific path. This leads to two questions:

• Should it send OBSERVED_ADDRESS frames for all paths together with PATH_CHALLENGE?
• Do we even send OBSERVED_ADDRESS frames for all paths anywhere right now?