Add new argument to hf_mailbox_send.

We don't do anything with it yet, but adding it in a separate patch
reduces the mix of functionality and refactor in the next patch.

Change-Id: I24cbd4d35c4cf9e4985a72d336a68c496c9cc2be
diff --git a/test/hftest/inc/hftest_impl.h b/test/hftest/inc/hftest_impl.h
index 3d4a44a..fa9e4c7 100644
--- a/test/hftest/inc/hftest_impl.h
+++ b/test/hftest/inc/hftest_impl.h
@@ -255,7 +255,7 @@
                                                                               \
 		/* Send the selected service to run and let it be handled. */ \
 		memcpy(send_buffer, service, strlen(service));                \
-		ASSERT_EQ(hf_mailbox_send(vm_id, strlen(service)), 0);        \
+		ASSERT_EQ(hf_mailbox_send(vm_id, strlen(service), false), 0); \
 		run_res = hf_vcpu_run(vm_id, 0);                              \
 		ASSERT_EQ(run_res.code, HF_VCPU_RUN_YIELD);                   \
 	} while (0)