wifi: Legacy HAL Thermal API stub

Add the stub implementation for Wifi thermal API

Bug: 140311866
Test: Manual, on device
Change-Id: I401bf7a38fa52d160ae45cd519a225c07360cd3c
diff --git a/wifi/1.4/default/wifi_legacy_hal.h b/wifi/1.4/default/wifi_legacy_hal.h
index 7f16c30..74cc84b 100644
--- a/wifi/1.4/default/wifi_legacy_hal.h
+++ b/wifi/1.4/default/wifi_legacy_hal.h
@@ -259,6 +259,9 @@
     virtual wifi_error resetTxPowerScenario(const std::string& iface_name);
     wifi_error setLatencyMode(const std::string& iface_name,
                               wifi_latency_mode mode);
+    wifi_error setThermalMitigationMode(const std::string& iface_name,
+                                        wifi_thermal_mode mode,
+                                        uint32_t completion_window);
     // Logger/debug functions.
     std::pair<wifi_error, uint32_t> getLoggerSupportedFeatureSet(
         const std::string& iface_name);