netxen: fix mac addr setup

For NX3031 mac addr should be read from firmware. mac addr in flash
is still valid, but can be overridden by firmware if running in
virtualization environment.

For old revisions, mac addr is retrieved directly from flash.

Signed-off-by: Dhananjay Phadke <dhananjay@netxen.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>