regression 1025: skip test if memref null capability not supported

Skip regression test 1025 when TEE context reports that memref null
capability is not supported by the OP-TEE ecosystem. This change
prevents xtest suite to fail on regression 1025 when one tests
the latest optee_os/optee_client/optee_test that supports this recent
capability with a mainline or older Linux kernel that does not yet
support this feature.

Fixes: https://github.com/OP-TEE/optee_test/issues/415
Reported-by: Masami Hiramatsu <masami.hiramatsu@linaro.org>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Acked-by: Jerome Forissier <jerome@forissier.org>
diff --git a/host/xtest/regression_1000.c b/host/xtest/regression_1000.c
index 17e15b2..5305c6a 100644
--- a/host/xtest/regression_1000.c
+++ b/host/xtest/regression_1000.c
@@ -1917,6 +1917,11 @@
 	uint32_t ret_orig = 0;
 	uint8_t *empty_buf = NULL;
 
+	if (!xtest_teec_ctx.memref_null) {
+		Do_ADBG_Log("Skip test: MEMREF_NULL capability not supported");
+		return;
+	}
+
 	if (!ADBG_EXPECT_TEEC_SUCCESS(c,
 				      xtest_teec_open_session(&session,
 							      &os_test_ta_uuid,