iwlwifi: warn when send tx power settings during scan

Add WARN_ONCE when scanning is pending. Use STATUS_SCAN_HW bit since we
can have scan canceled or completed but STATUS_SCANNING bit still set.

v1 -> v2: replace EIO to EAGAIN

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-agn-lib.c b/drivers/net/wireless/iwlwifi/iwl-agn-lib.c
index b555edd..5e3d799 100644
--- a/drivers/net/wireless/iwlwifi/iwl-agn-lib.c
+++ b/drivers/net/wireless/iwlwifi/iwl-agn-lib.c
@@ -496,6 +496,10 @@
 	struct iwlagn_tx_power_dbm_cmd tx_power_cmd;
 	u8 tx_ant_cfg_cmd;
 
+	if (WARN_ONCE(test_bit(STATUS_SCAN_HW, &priv->status),
+		      "TX Power requested while scanning!\n"))
+		return -EAGAIN;
+
 	/* half dBm need to multiply */
 	tx_power_cmd.global_lmt = (s8)(2 * priv->tx_power_user_lmt);