It's proliferated throughout three .c files so let's pull them all
together in gre.h where the inline function belongs. This requires
some adjustments to the compat layer so that the various iterations
of gre_calc_hlen and ip_gre_calc_hlen since the 3.10 kernel are
handled correctly.
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
Acked-by: William Tu <u9012063@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>