Workaround wickedd problem (bnc#900112)

By enabling tx-offloading in the network barclamp we avoid having the
ETHTOOL_OPTIONS added to the ifcfg files. This works around:
https://bugzilla.suse.com/show_bug.cgi?id=900112
Merge pull request #131 from rhafer/bnc900112

Workaround wickedd problem (bnc#900112)