Silently fall back to the guess the IP address with a remote server

Silently fall back to the guess the IP address with a remote server

For most OSes we do not implement a way to read the current IP
address from the local configuration. In that case ddns used to
throw an exception and stop. This patch changes that in the way
that ddns will fall back to guess the IP address with help
of a remote server.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>