Proposed by and based on a patch from Eric Dumazet <dada1@cosmosbay.com>:
This patch removes unnecessary critical section in ksize() function, as 
cli/sti are rather expensive on modern CPUS.
It additionally adds a docbook entry for ksize() and further simplifies 
the code.

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>