This patch add the latency to the nodewatcher data.
The target of the ping can configure in /etc/config/fff
Example:
config latency 'latency'
option ipv4 'ff1.zbau.f3netze.de'
option ipv6 'ff1.zbau.f3netze.de'
if no target is set, no latency is send.
Signed-off-by: Christian Dresel <freifunk@dresel.systems>