fix: sublevel version overflow in LINUX_VERSION_CODE

fix: sublevel version overflow in LINUX_VERSION_CODE

The 4.4.256 and 4.9.256 stable release overflow the 8bits allocated to
the sublevel in LINUX_VERSION_CODE which ends means they report
themselves as 4.5.0 and 4.10.0 respectively. The next releases in these
stables branches will have sublevel clamped at 255 and will thus report
themselves as 4.4.255 and 4.9.255 for all subsequent releases.

We need a way to way to properly detect these release since I doubt they
will stop breaking tracepoints declarations. As a workaround, extract
the version information from the Makefile in the kernel headers and use
this information to generate a version code when the sublevel is equal
or greater than 256.

Change-Id: I96ae9f22c0c1ba8c619643946a5311c767fbcf8c
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>