qlcnic: Limit vNIC support in legacy interrupt mode

o When the driver loads in legacy interrupt mode, only vNICs
  with PCI function number 0-7 are supported.

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