compat: deactivate netdev_set_default_ethtool_ops() for some 3.7 kernels

Upstream commit 4971ae5e2075a284ff36a68cab7c3f407a852801

netdev_set_default_ethtool_ops() was backported in 3.7.8 and compat
should not ship it on any more recent versions any more.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>