can: dump stack on protocol bugs

The rework of the kernel hlist implementation "hlist: drop the node parameter
from iterators" (b67bfe0d42cac56c512dd5da4b1b347a23f4b70a) created some
fallout in the form of non matching comments and obsolete code.

Additionally to the cleanup this patch adds a WARN() statement to catch the
caller of the wrong filter removal request.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: David S. Miller <davem@davemloft.net>