dgram (udp) catchup with runtime/pull/595

Should be ready, but does require coordinated release with <del>https://github.com/tessel/runtime/pull/595</del><ins>https://github.com/tessel/runtime/pull/622</ins>.
THIS IS WHAT YOU GET IF YOU STRIP INDENTS FROM BLANK LINES AND THEN ALSO USE TABS INSTEAD OF SPACES LIKE ALL THE OTHER REPOS I HOPE YOU ARE HAPPY