Added disable_offload parameter

By default, we don't touch physical nic settings.
However, it is better to disable generic segmentation offload (gso)
and generic receive offload (gro). See ethtool man for details.

Related fuel-web patch: I24fdb63bab9166720862b4f6c96b90f6cd1d5f8c

DocImpact
Change-Id: I69fa29757557ed5337239031bf22d127e4a4edf6
Closes-bug: 1275650
Merge "Added disable_offload parameter"