Updated firmware on my router, that added a new option MLG (multicast listener directory).
I set my router for IGMP Snooping = on, and MLG Snooping = on.
t2 list # no results
switched to @HipsterBrown branch...
t2 list # yay, got my tessel!
So its a good result for me, although a little painful that it required not only a config change on my router, but also a firmware update (although I was only one update behind and the last one was issued in 2013, which gives away the age of my router a little)