qlcnic: enable mac-learning in promiscous mode.

MAC learning is required in bridge mode.
During bridge mode device will be put in promiscous mode.

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>