Ask the peer who sent us the DSRM for the RouterInfos...
... but If we have the routerInfo already, try to refetch it from that router itself,
(if the info is old or we don't think it is floodfill)
which will help us establish that router as a good floodfill and speed our
integration into the network.
Very similar to SingleLookupJob.
This was all in IterativeLookupSelector.isMatch() but it caused deadlocks
at both _search.newPeerToTry() and _search.failed().