network: Fix udev information caching

Previously the caching of the udev informations was done wrong, which
lead to problems in the UI (shoing no or outdated informations).
This patch fixes the caching behavior.

Change-Id: I56efb7bee409682ae102229f338f7cb8eb6b7cb0
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=978226
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>