orinoco: Add ESSID specific scanning for Agere fw

Pass the ESSID to the card.

This allows 'iwlist eth1 scan essid <essid>' to work, and will help
with routers setup not to broadcast the ESSID.

Signed-off-by: David Kilroy <kilroyd@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>