Rethtool executes two ioctls SIOCETHTOOL, one with
command ETHTOOL_GLINKSETTINGS and then with ETHTOOL_GDRVINFO,
but some drivers (like virtio) don't implement
ETHTOOL_GLINKSETTINGS, so it fails.
I've send patch to the author of Rethtool, but he haven't
replied yet, and it also will take some time to have this
fix in out Rethtool package. So let's call ioctl
seaprately if Rethtool::InterfaceSettings failed.
Change-Id: Iea95e1b132a33621f7538c4b0ba43b134e2560ee
c5d6963e04