Fixed setting kafka's advertised IP

Shortly before pushing the latest API I did some refactoring. During
that I unfortunately broke this.
The advertised IP has to be without subnet mask. So we remove it here if
one was existing.

Change-Id: I37f9df376d0c899b4911b23302dacb9922122f0f
Signed-off-by: schillinge <ablu@mail.uni-paderborn.de>