netxen: avoid frequent firmware reset

Restrict firmware reset to following cases -

o chip rev is NX2031 (firmare doesn't support heartbit).
o firmware is dead.
o previous attempt to init firmware had failed.
o we have got newer file firmware.

This speeds up module load tremendously (by upto 8 sec),
also avoids downtime for NCSI (management) pass-thru
traffic.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>