Imports initializates cache in NetworkInterfaces. bnc#817797

Import into NetworkInterfaces didn't set an update flag. Imported data
could be overwritten by subsequent Read.

Normal SLES installation was not affected. Issue was observed for
OES which calls NetworkInterfaces::Read in an AddOn.
Updated changelog
Merge pull request #87 from mchf/Code-11-SP3

NetworkInterfaces::Import sets cache initialized flag.