Added 'disable generic offload' checkbox

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-library patch: I69fa29757557ed5337239031bf22d127e4a4edf6

DocImpact
Change-Id: I24fdb63bab9166720862b4f6c96b90f6cd1d5f8c
Closes-Bug: 1275650
Merge "Added 'disable generic offload' checkbox"