Add latency metrics to sip pings

Can we add latency measurement. Would be great to have loss info alongside latency. Shd be as simple as recording start and stop time between socket send and recv.
Ref: https://github.com/laurieodgers/sipping/blob/f1fc789989faf2436f0e4f0499b5fe36527b43a1/sipping.py#L95