Wrap compound native_handle_t* in hidl_pointer.

When transferring a handle in a compound type,
we need to use hidl_pointer<> to ensure that we
allocate enough space for the pointer. But we want
to hide the hidl_pointer<> type from client/server
code as much as we can, so we only use this type
when necessary (eg when the handle is embedded in
a struct).

Bug: 32089785
Test: builds
Change-Id: I30c9aa9f1348fd5e72cd6d1e71d9ac3b4bd8ea8e
diff --git a/Interface.cpp b/Interface.cpp
index 9f5351c..35cbce3 100644
--- a/Interface.cpp
+++ b/Interface.cpp
@@ -217,6 +217,7 @@
     switch (mode) {
         case StorageMode_Stack:
         case StorageMode_Result:
+        case StorageMode_Compound:
             return base;
 
         case StorageMode_Argument: