compat: backport BUILD_BUG_ON from recent kernel

This version of BUILD_BUG_ON does not have the following error on an
old kernel version (2.6.32 - 2.6.37):

drivers/net/wireless/iwlwifi/mvm/quota.c:145:24: error: bit-field
'<anonymous>' width not an integer constant

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: netdev_set_default_ethtool_ops() is not in kernel 3.7.5

netdev_set_default_ethtool_ops() should be added to compat for every
3.7.X series kernel as it is also not in 3.7.5.