ath9k: connectivity is lost after Group rekeying is done

Connectivtiy is lost after Group rekeying is done. The keytype
maintained by ath9k is reset when group key is updated. Though
sc_keytype can be reset only for broadcast key the proper fix
would be to use mac80211 provided key type from txinfo during
xmit and get rid of sc_keytype from ath9k ath_softc.

Signed-off-by: Vasanthakumar Thiagarajan <vasanth@atheros.com>
Signed-off-by: Senthil Balasubramanian <senthilkumar@atheros.com>
Tested-by: Steven Noonan <steven@uplinklabs.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>