compat: include linux/compat-3.8.h

This header file was not included in this branch.
This also fixes a compile problem in linux/compat-3.8.h.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
compat: add compat/compat-3.8.c

compat/compat-3.8.c was never build and had a compile error which is
fixed now.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
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>
compat: add include/export.h in compat-3.8.c

This is not indirectly included on some kernel versions

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