qlcnic: Fix SR-IOV configuration

o Interface needs to be brought down and up while configuring SR-IOV.
  Protect interface up/down using rtnl_lock()/rtnl_unlock()

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