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/hostcmd.h b/drivers/net/wireless/libertas/hostcmd.h
index 913b480..7f155cd 100644
--- a/drivers/net/wireless/libertas/hostcmd.h
+++ b/drivers/net/wireless/libertas/hostcmd.h
@@ -435,8 +435,12 @@
 };
 
 struct cmd_ds_802_11_rf_tx_power {
+	struct cmd_header hdr;
+
 	__le16 action;
-	__le16 currentlevel;
+	__le16 curlevel;
+	s8 maxlevel;
+	s8 minlevel;
 };
 
 struct cmd_ds_802_11_rf_antenna {
@@ -701,7 +705,6 @@
 		struct cmd_ds_802_11_get_stat gstat;
 		struct cmd_ds_802_3_get_stat gstat_8023;
 		struct cmd_ds_802_11_snmp_mib smib;
-		struct cmd_ds_802_11_rf_tx_power txp;
 		struct cmd_ds_802_11_rf_antenna rant;
 		struct cmd_ds_802_11_monitor_mode monitor;
 		struct cmd_ds_802_11_ad_hoc_join adj;