rt2x00: Move bssidx calculation into its own function

This will be used by a later patch. No functional changes.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/rt2x00/rt2x00mac.c b/drivers/net/wireless/rt2x00/rt2x00mac.c
index 4ccf238..9db9378 100644
--- a/drivers/net/wireless/rt2x00/rt2x00mac.c
+++ b/drivers/net/wireless/rt2x00/rt2x00mac.c
@@ -504,15 +504,7 @@
 
 	memset(&crypto, 0, sizeof(crypto));
 
-	/*
-	 * When in STA mode, bssidx is always 0 otherwise local_address[5]
-	 * contains the bss number, see BSS_ID_MASK comments for details.
-	 */
-	if (rt2x00dev->intf_sta_count)
-		crypto.bssidx = 0;
-	else
-		crypto.bssidx = vif->addr[5] & (rt2x00dev->ops->max_ap_intf - 1);
-
+	crypto.bssidx = rt2x00lib_get_bssidx(rt2x00dev, vif);
 	crypto.cipher = rt2x00crypto_key_to_cipher(key);
 	if (crypto.cipher == CIPHER_NONE)
 		return -EOPNOTSUPP;