Staging: batman-adv: Calculate hamming weight using optimized kernel functions

The Kernighan algorithm is not able to calculate the number of set bits
in parallel and the compiler cannot replace it with optimized
instructions.

The kernel provides specialised functions for each cpu which can either
use a software implementation or hardware instruction depending on the
target cpu.

Reported-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --cc drivers/staging/batman-adv/TODO
Simple merge

diff --cc drivers/staging/batman-adv/bitarray.c
Simple merge

diff --cc drivers/staging/batman-adv/bitarray.h
Simple merge