qlcnic: fix multicast handling

For promiscuous mode, driver send request to device for deleting
multicast addresses and again it send request for adding them back
while exiting from this mode, this is bad for performance.
Just setting device in promiscuous mode is enough, no need to del/add
multicast addresses.

Signed-off-by: Sucheta Chakraborty <sucheta.chakraborty@qlogic.com>
Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>