test vlan: Fix race condition on MAC address

When creating VLAN parent dummy interface without `address` property
defined, systemd/udevd will generate random MAC address and change it,
hence we have race problem during creation and query.

Fixed by explicitly set MAC address when creating VLAN parent interface
in tests.

Signed-off-by: Gris Ge <cnfourt@gmail.com>

Author: cathay4t

src/ip/link/tests/vlan.rs

@@ -247,7 +247,15 @@ where
     let parent_name = format!("p{vlan_name}");
 
     // create parent dummy interface using ip-rs
-    ip_rs_exec_cmd(&["link", "add", &parent_name, "type", "dummy"]);
+    ip_rs_exec_cmd(&[
+        "link",
+        "add",
+        &parent_name,
+        "address",
+        "0e:d1:49:08:27:84",
+        "type",
+        "dummy",
+    ]);
     exec_cmd(&["ip", "link", "set", &parent_name, "up"]);
 
     let mut args = vec![