[PATCH] forcedeth: Initialize link settings in every nv_open()

Rüdiger found a bug in nv_open that explains some of the reports
with duplex mismatches:
nv_open calls nv_update_link_speed for initializing the hardware link speed
registers. If current link setting matches the values in np->linkspeed and
np->duplex, then the function does nothing.
Usually, doing nothing is the right thing, but not in nv_open: During
nv_open, the registers must be initialized because the nic was reset.

The attached patch fixes that by setting np->linkspeed to an invalid value
before calling nv_update_link_speed from nv_open.

Signed-Off-By: Manfred Spraul <redacted>