ping deviation report negative number if rtt reaches 8 min.

[Stefan Helmert]

On Ubuntu 16.04.2: If ping time reaches 8 min. with over 600 echo requests on a lossy internet access, an overflow can happen resulting in a negative mdev value.

The second bug triggered by this bug shows a minus sign after the decimal separator.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: iputils-ping 3:20121221-5ubuntu2
ProcVersionSignature: Ubuntu 4.4.0-81.104-generic 4.4.67
Uname: Linux 4.4.0-81-generic x86_64
NonfreeKernelModules: nvidia_uvm nvidia_drm nvidia_modeset nvidia
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
CurrentDesktop: Unity
Date: Sun Jun 25 22:08:25 2017
SourcePackage: iputils
UpgradeStatus: No upgrade log present (probably fresh install)

[David Heidelberg (okias)]

Could you check latest upstream version? [1]

Lastest commit in branch negative_fix should make it OK :)

Please report, thank you!

[1] https://github.com/iputils/iputils/commits/negative_fix