Pinger.run() should return immediately when packet recieved

[woodsaj]

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

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

[woodsaj]

This change also ensures that OnIdle() is only called when MaxRTT is reached and no packet has been received.

[traveller42]

This could have detrimental effects if one is pinging multiple targets.

[kanocz]

It's possible, but only with bigger changes that breaks compatibility with original version, like I have in https://github.com/kanocz/go-fastping :-(

[harshitha-bt]

So this is not yet fixed in this repo right?