Bluetooth: Host: Fix unable to start scanning after scan param failure

Fix scan_update() implementation for missing flags clear
that prevented starting scanning after previous attempt to
start failed due to parameters being rejected by the
Controller.

Example, attempting to start coded PHY scanning with a
Controller implementation that does not support it can fail,
but attempting again without coded PHY scanning should
succeed.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>

Author: cvinayak

subsys/bluetooth/host/scan.c

@@ -476,7 +476,7 @@ static int scan_update(void)
 	return err;
 }
 
-static uint32_t scan_check_if_state_allowed(enum bt_le_scan_user flag)
+static int scan_check_if_state_allowed(enum bt_le_scan_user flag)
 {
 	/* check if state is already set */
 	if (atomic_test_bit(scan_state.scan_flags, flag)) {
@@ -499,16 +499,22 @@ int bt_le_scan_user_add(enum bt_le_scan_user flag)
 		/* Only check if the scanner parameters should be updated / the scanner should be
 		 * started. This is mainly triggered once connections are established.
 		 */
-	} else {
-		/* Check if it can be enabled */
-		err = scan_check_if_state_allowed(flag);
-		if (err) {
-			return err;
-		}
-		atomic_set_bit(scan_state.scan_flags, flag);
+		return scan_update();
 	}
 
-	return scan_update();
+	err = scan_check_if_state_allowed(flag);
+	if (err) {
+		return err;
+	}
+
+	atomic_set_bit(scan_state.scan_flags, flag);
+
+	err = scan_update();
+	if (err) {
+		atomic_clear_bit(scan_state.scan_flags, flag);
+	}
+
+	return err;
 }
 
 int bt_le_scan_user_remove(enum bt_le_scan_user flag)