Adding ring size to index calculation is pointless, since index
will be masked with ring size - 1.
Suggested-by: NDavid Laight <David.Laight@ACULAB.COM>
Signed-off-by: NJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>