xenomai: bump to 2.6.1

The largefile patch is no longer necessary, it has been merged
upstream. However, in order to make the build work properly with
Thumb2 toolchains (such as Linaro toolchains), an additional fix is
needed. This fix is already upstream and will be part of upcoming
Xenomai releases.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>