rt2x00: txdone implementation supporting hw encryption.

This is an implementation that support WCID being the encryption key.
Wireless Cli Id was set to be the encryption key in rt2800pci_write_tx_desc
and read (TX_STA_FIFO_WCID) as the current queue entry index.

Signed-off-by: Benoit Papillault <benoit.papillault@free.fr>
Signed-off-by: Alban Browaeys <prahal@yahoo.com>
Acked-by: Ivo van Doorn <ivdoorn@gmail.com>
Signed-off-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>