tg3: Expand multicast drop counter miscounting fix to 5762

commit 4d958473 - "tg3: Workaround
rx_discards stat bug", added a workaround for miscounted statistics for
multicast packets. This fix needs to be applied to the 5762.

Signed-off-by: Nithin Nayak Sujir <nsujir@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>