qlcnic: Fix setting MAC address

o Delete previous unicast MAC which is already programmed
  in adapter before setting new unicast MAC

Signed-off-by: Manish Chopra <manish.chopra@qlogic.com>
Signed-off-by: Shahed Shaikh <shahed.shaikh@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>