[collectd] Ping plugin - IPv4/6

[Phil Endecott]

Dear Experts,

After an update from Debian stretch to buster, which I think
means collectd 5.7.1 to 5.8.1, some of my pings have stopped
working.  I think this is possibly because collectd is now
using IPv6 for some hosts, though I'm not certain of that.

In order to investigate further, it would be great if the
ping plugin had a setting to determine whether to use IPv4 or
IPv6.  It seems that liboping does have a setting for that,
so perhaps it would not be difficult to add.


Regards, Phil.