rpcss: Use I_Rpc(Free|Allocate) in MIDL_user_(allocate|free).

In ept_map, rpcss uses TowerConstruct to allocate tower array elements.

The array is later released by the generated stub code, and each element
is ultimately freed using MIDL_user_free.

TowerConstruct always allocate memory using I_RpcAllocate, we must use
I_RpcFree to free it.

programs/rpcss/irotp.c

@@ -368,10 +368,10 @@ void __RPC_USER IrotContextHandle_rundown(IrotContextHandle ctxt_handle)
 
 void * __RPC_USER MIDL_user_allocate(SIZE_T size)
 {
-    return malloc(size);
+    return I_RpcAllocate(size);
 }
 
 void __RPC_USER MIDL_user_free(void * p)
 {
-    free(p);
+    I_RpcFree(p);
 }