Enable ipv6 check in locked_rebuild()
Change locked_needsRebuild() to return codes for ipv4/v6
Change locked_needsRebuild() for introducers so it only
returns true if more are available
Change rebuildExternalAddress() so we can do a rebuild of ipv6 without an IP
Only call rebuildIfNecessary() on peer drop if it could have been an introducer
Fix check in pickInbound() for support of AliceIP field
Log tweaks