libertas: convert CMD_802_11_RF_TX_POWER to a direct command

And while we're at it, grab min/max TX power from the firmware and use
that to validate incoming TX power requests from WEXT.

Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas/main.c b/drivers/net/wireless/libertas/main.c
index bd32ac0..3c13619 100644
--- a/drivers/net/wireless/libertas/main.c
+++ b/drivers/net/wireless/libertas/main.c
@@ -956,17 +956,24 @@
 static int lbs_setup_firmware(struct lbs_private *priv)
 {
 	int ret = -1;
+	s16 curlevel = 0, minlevel = 0, maxlevel = 0;
 
 	lbs_deb_enter(LBS_DEB_FW);
 
-	/*
-	 * Read MAC address from HW
-	 */
+	/* Read MAC address from firmware */
 	memset(priv->current_addr, 0xff, ETH_ALEN);
 	ret = lbs_update_hw_spec(priv);
 	if (ret)
 		goto done;
 
+	/* Read power levels if available */
+	ret = lbs_get_tx_power(priv, &curlevel, &minlevel, &maxlevel);
+	if (ret == 0) {
+		priv->txpower_cur = curlevel;
+		priv->txpower_min = minlevel;
+		priv->txpower_max = maxlevel;
+	}
+
 	lbs_set_mac_control(priv);
 done:
 	lbs_deb_leave_args(LBS_DEB_FW, "ret %d", ret);