New IP-address of 'ping.ipfire.org'

New IP-address of 'ping.ipfire.org'

Telekom gateways (e.g.) don't answer 'pings', therefor '/etc/ppp/ip-up'
uses 'ping.ipfire.org' for the 'gateway Graph' in 'Status / Network (other'.
After moving the infrastructure, several IP addresses were changed.
'178.63.73.246' doesn't work anymore for 'ping.ipfire.org', its now '81.3.27.38'.

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>