netxen: add fw version compatibility check

o Minimum fw version supported for P3 chip is 4.0.505
o File Fw > 4.0.554 is not supported if flash fw < 4.0.554.
o In mn firmware case, file fw older than flash fw is allowed.
o Change variable names for readability
o Update driver version 4.0.76

Signed-off-by: Amit Kumar Salecha <amit.salecha@qlogic.com>
Signed-off-by: David S. Miller <davem@davemloft.net>