baseboxd: ensure knet is available before trying to use it
baseboxd: ensure knet is available before trying to use it

Add a small check for the knet /proc interface being available before
trying to use it, and fall back to TAP interfaces in case it isn't.

Signed-off-by: Jonas Gorski <9712c064bde5a52658fc87d6454b4956f9bf286b@bisdn.de>

bisdn/basebox,bisdn/basebox,bisdn/basebox,bisdn/basebox