Some code already uses ip_hdr() functions which did not exist in
2.6.21 and I do not feel like adding more compat code.
Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
The extension modules use the API of a fairly recent kernel, if not
even the networking git tree. To make it work with older Linux
kernels, an API wrapper is added. Should compile against
running-kernels Linux 2.6.19..current (tested: 2.6.22..current).
Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>
