tests: net: vlan: Fix VLAN disable test

Because we now return first non VLAN interface if found, the
VLAN disable test case needs adjustment.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
diff --git a/tests/net/vlan/src/main.c b/tests/net/vlan/src/main.c
index 88a0144..4cc402e 100644
--- a/tests/net/vlan/src/main.c
+++ b/tests/net/vlan/src/main.c
@@ -566,14 +566,14 @@
 	eth_ctx = net_if_l2_data(eth_interfaces[0]);
 
 	iface = net_eth_get_vlan_iface(eth_interfaces[0], VLAN_TAG_1);
-	zassert_equal_ptr(iface, NULL,
+	zassert_equal_ptr(iface, eth_interfaces[0],
 			  "Invalid interface for tag %d (%p vs %p)\n",
-			  VLAN_TAG_1, iface, NULL);
+			  VLAN_TAG_1, iface, eth_interfaces[0]);
 
 	iface = net_eth_get_vlan_iface(eth_interfaces[0], VLAN_TAG_2);
-	zassert_equal_ptr(iface, NULL,
+	zassert_equal_ptr(iface, eth_interfaces[0],
 			  "Invalid interface for tag %d (%p vs %p)\n",
-			  VLAN_TAG_2, iface, NULL);
+			  VLAN_TAG_2, iface, eth_interfaces[0]);
 
 	ret = net_eth_is_vlan_enabled(eth_ctx, eth_interfaces[0]);
 	zassert_equal(ret, false, "VLAN enabled for interface 0\n");