wifi: Duplicate getValidChannelsForBand in AP iface

This functionality is needed even for AP iface. So, duplicate this
method.

Changes in the CL:
1. Add getValidChannelsForBand() in IWifiApIface.
2. Rename StaBackgroundScanBan to WifiBand to make it a more generic
name.
3. Change the existing method name in IWifiStaIface to match with the
one in IWifiApIface.

While there,
Fix indentation in hidl_callback_util.h

Bug: 35663149
Test: Compiles
Change-Id: Iaeb6c323e13eedf2f98de92fea77e327c76ffa5b
diff --git a/wifi/1.0/default/hidl_struct_util.cpp b/wifi/1.0/default/hidl_struct_util.cpp
index 7dbc8eb..c7b8c41 100644
--- a/wifi/1.0/default/hidl_struct_util.cpp
+++ b/wifi/1.0/default/hidl_struct_util.cpp
@@ -306,21 +306,21 @@
   return true;
 }
 
-legacy_hal::wifi_band convertHidlGscanBandToLegacy(StaBackgroundScanBand band) {
+legacy_hal::wifi_band convertHidlWifiBandToLegacy(WifiBand band) {
   switch (band) {
-    case StaBackgroundScanBand::BAND_UNSPECIFIED:
+    case WifiBand::BAND_UNSPECIFIED:
       return legacy_hal::WIFI_BAND_UNSPECIFIED;
-    case StaBackgroundScanBand::BAND_24GHZ:
+    case WifiBand::BAND_24GHZ:
       return legacy_hal::WIFI_BAND_BG;
-    case StaBackgroundScanBand::BAND_5GHZ:
+    case WifiBand::BAND_5GHZ:
       return legacy_hal::WIFI_BAND_A;
-    case StaBackgroundScanBand::BAND_5GHZ_DFS:
+    case WifiBand::BAND_5GHZ_DFS:
       return legacy_hal::WIFI_BAND_A_DFS;
-    case StaBackgroundScanBand::BAND_5GHZ_WITH_DFS:
+    case WifiBand::BAND_5GHZ_WITH_DFS:
       return legacy_hal::WIFI_BAND_A_WITH_DFS;
-    case StaBackgroundScanBand::BAND_24GHZ_5GHZ:
+    case WifiBand::BAND_24GHZ_5GHZ:
       return legacy_hal::WIFI_BAND_ABG;
-    case StaBackgroundScanBand::BAND_24GHZ_5GHZ_WITH_DFS:
+    case WifiBand::BAND_24GHZ_5GHZ_WITH_DFS:
       return legacy_hal::WIFI_BAND_ABG_WITH_DFS;
   };
   CHECK(false);