ping_once should return immediately when packet recieved

[EnverOsmanov]

The idea is already described in another issue, so I will paste an adapted quote:

Regardless of the latency of the ICMP packets, Pinger.run_once() currently only returns after MaxRTT.

I understanding using MaxRTT to space pings when running with run_pinger(), but when i explicitly call Pinger.ping_once(), I want it to return as soon as the response ICMP packet is received.