emard<at>softhome!net discovered an embarrasing bug in dvb_net.c where
the NET_REMOVE_IF ioctl will cause an Oops when called with an invalid
interface number. 
Signed-off-by: Johannes Stezenbach <js@linuxtv.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>