tg3: LED in shared mode does not blink during traffic

On the 5717, 5719, 5720 and 5762 devices, in shared link/activity mode,
the blink rate must be overridden with all bits set.

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>