A 2's complement subtraction will always do a borrow, so masking
off the sign bits is the same as conditionally adding (mask+1).
Signed-off-by: NDoug Berger <opendmb@gmail.com>
Reviewed-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>