bnx2x: ethtool now returns unknown speed/duplex

Previously, unless both interface and link were up, ethtool returned
the requested speed/duplex when asked for the interface's settings.
This change will now enable the driver to answer correctly (i.e.,
return unknown as its answer).

Signed-off-by: Yuval Mintz <yuvalmin@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>