message: [dbus] fix link counter values
  Some link counters are assigned with wrong values in DBus API.
diff: @@ -801,10 +801,10 @@ otError DBusThreadObject::GetLinkCountersHandler(DBusMessageIter &aIter)
  counters.mTxErrAbort = otCounters->mTxErrAbort;
  counters.mTxErrBusyChannel = otCounters->mTxErrBusyChannel;
  counters.mRxTotal = otCounters->mRxTotal;
  - counters.mRxUnicast = otCounters->mTxUnicast;
  + counters.mRxUnicast = otCounters->mRxUnicast;
  counters.mRxBroadcast = otCounters->mRxBroadcast;
  counters.mRxData = otCounters->mRxData;
  - counters.mRxDataPoll = otCounters->mTxDataPoll;
  + counters.mRxDataPoll = otCounters->mRxDataPoll;
  counters.mRxBeacon = otCounters->mRxBeacon;
  counters.mRxBeaconRequest = otCounters->mRxBeaconRequest;
  counters.mRxOther = otCounters->mRxOther;
  