Move setScanMode to legacy HAL

Cherry-pick from https://partner-android-review.git.corp.google.com/c/platform/hardware/interfaces/+/2369946
Implementation of setScanMode is platform-specific. It's more reasonable to move it the legacy HAL like other platform-specific APIs.

Bug: 265866990
Test: manual Test
Test: VTS
Change-Id: I2f8ff73b764ed1b9835b8e3157f673d7d558ae02
diff --git a/wifi/aidl/default/wifi_legacy_hal.h b/wifi/aidl/default/wifi_legacy_hal.h
index 1e6ef73..a066ea6 100644
--- a/wifi/aidl/default/wifi_legacy_hal.h
+++ b/wifi/aidl/default/wifi_legacy_hal.h
@@ -741,6 +741,8 @@
 
     wifi_error twtClearStats(const std::string& iface_name, uint8_t configId);
 
+    wifi_error setScanMode(const std::string& iface_name, bool enable);
+
     wifi_error setDtimConfig(const std::string& iface_name, uint32_t multiplier);
 
     // Retrieve the list of usable channels in the requested bands