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_callback_util.h b/wifi/1.0/default/hidl_callback_util.h
index a1c6819..7136279 100644
--- a/wifi/1.0/default/hidl_callback_util.h
+++ b/wifi/1.0/default/hidl_callback_util.h
@@ -82,14 +82,12 @@
     return true;
   }
 
-  const std::set<android::sp<CallbackType>> getCallbacks() {
-    return cb_set_;
-  }
+  const std::set<android::sp<CallbackType>> getCallbacks() { return cb_set_; }
 
   // Death notification for callbacks.
   void onObjectDeath(uint64_t cookie) {
-    CallbackType *cb = reinterpret_cast<CallbackType*>(cookie);
-    const auto& iter =  cb_set_.find(cb);
+    CallbackType* cb = reinterpret_cast<CallbackType*>(cookie);
+    const auto& iter = cb_set_.find(cb);
     if (iter == cb_set_.end()) {
       LOG(ERROR) << "Unknown callback death notification received";
       return;