kernel: backport switch user API changes after r36283

3.3 and 3.6 kernels do not make use of the UAPI headers, still they need
to provide an up-to-date switch.h copy for swconfig to build.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@36295 3c298f89-4303-0410-b956-a3cf2f4a3e73