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/wifi_ap_iface.h b/wifi/1.0/default/wifi_ap_iface.h
index 23d6435..efc168a 100644
--- a/wifi/1.0/default/wifi_ap_iface.h
+++ b/wifi/1.0/default/wifi_ap_iface.h
@@ -44,12 +44,16 @@
   Return<void> getType(getType_cb hidl_status_cb) override;
   Return<void> setCountryCode(const hidl_array<int8_t, 2>& code,
                               setCountryCode_cb hidl_status_cb) override;
+  Return<void> getValidFrequenciesForBand(
+      WifiBand band, getValidFrequenciesForBand_cb hidl_status_cb) override;
 
  private:
   // Corresponding worker functions for the HIDL methods.
   std::pair<WifiStatus, std::string> getNameInternal();
   std::pair<WifiStatus, IfaceType> getTypeInternal();
   WifiStatus setCountryCodeInternal(const std::array<int8_t, 2>& code);
+  std::pair<WifiStatus, std::vector<WifiChannelInMhz>>
+  getValidFrequenciesForBandInternal(WifiBand band);
 
   std::string ifname_;
   std::weak_ptr<legacy_hal::WifiLegacyHal> legacy_hal_;