track peer traffic and expose via admin function

Ok, I revised this as I couldn't figure out how to get access to the peer info from the SwitchCore so I moved it into the InterfaceController.

example:
```
$ ./contrib/python/cexec 'InterfaceController_peerStats()'
{'count': 1, 'peers': [{'state': 2, 'bytesOut': 7874, 'pubkey': 'rs3z4ks50znnkl5guqrlb6xcf7bgu3unz14v2w9t2sq5tv6cls10.k', 'bytesIn': 15864}], 'txid': '8P3TJQTT73'}
```