be2net: Fix to apply duplex value as unknown when link is down.

Suggested-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Sarveshwar Bandi <sarveshwar.bandi@emulex.com>
Signed-off-by: Somnath Kotur <somnath.kotur@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>