netxen_nic: Avoid mixed mode interrupts

o Adapters do not support co-existence of INTx Interrupt with
  MSI-X or MSI among multiple functions. Prevent attaching
  of a function during normal load, if adapter gets into mixed
  mode of interrupts

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