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/IWifiApIface.hal b/wifi/1.0/IWifiApIface.hal
index aeca2cd..1f6ee7c 100644
--- a/wifi/1.0/IWifiApIface.hal
+++ b/wifi/1.0/IWifiApIface.hal
@@ -33,4 +33,21 @@
    *         |WifiStatusCode.FAILURE_IFACE_INVALID|
    */
   setCountryCode(int8_t[2] code) generates (WifiStatus status);
+
+  /**
+   * Used to query the list of valid frequencies (depending on country code set)
+   * for the provided band.
+   *
+   * @param band Band for which the frequency list is being generated.
+   * @return status WifiStatus of the operation.
+   *         Possible status codes:
+   *         |WifiStatusCode.SUCCESS|,
+   *         |WifiStatusCode.ERROR_WIFI_IFACE_INVALID|,
+   *         |WifiStatusCode.ERROR_NOT_SUPPORTED|,
+   *         |WifiStatusCode.ERROR_NOT_AVAILABLE|,
+   *         |WifiStatusCode.ERROR_UNKNOWN|
+   * @return frequencies vector of valid frequencies for the provided band.
+   */
+  getValidFrequenciesForBand(WifiBand band)
+      generates (WifiStatus status, vec<WifiChannelInMhz> frequencies);
 };