dgram tests/improvements

Also requires https://github.com/tessel/firmware/pull/104. Should be ready now.
In this case node.js gives one a bad time if one elects to make up their own docs: https://github.com/joyent/node/blob/029cfc12a0736b0b03d0101d24b8a1a3023137a5/lib/dgram.js#L57 :cake: