qlcnic: Fix loopback test for SR-IOV PF.

o Do not disable mailbox interrupts while running
  loopback test through SR-IOV PF.

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