BUG10941: fix single ip-addresses when no subnet given

BUG10941: fix single ip-addresses when no subnet given

Some functions when adding a new route where senseless.
Now the ip address is checked and in case of a missing / wrong
subnetmask an errormessage is raised. The ip address is preserved.
ELSE
we convert the subnetmask to cidr notation and calculate the network ip
correctly.

Signed-off-by: Alexander Marx <alexander.marx@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>