Update copies of linux/dcbnl.h and src/linux/if_link.h to 3.15.1

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Add copies of linux/ethtool.h and linux/if_tunnel.h from 3.15.1

Signed-off-by: Olaf Hering <olaf@aepfle.de>
Merge pull request #353 from olafhering/olh-misc

Upgrade included linux headers to 3.15