net: mv88e6xxx: Fix ingress rate removal for mv6131 chips

The PORT_RATE_CONTROL register works differently on 88e6095/6095f/6131
in comparison to 6123/61/65, and 0x0 disables. The distinction was lost
Linux 4.1 --> 4.2

Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>