linknx: new package

[Peter: add patch to fix build issue with gcc 4.7+]
[Thomas: various fixes/improvements]
Signed-off-by: Gregory Hermant <gregory.hermant@calao-systems.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>