netxen: fix detection of cut-thru firmware mode

Fix the detection of cut-thru mode of the hardware (direct dma
to host) to mode configured in SRE (ingress block) rather than
onboard memory control.

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