conf: duplicate interface name instead of MAC provided to lookup the interface

Introduced by 6094d6ec.
Found by running libvirt-perl tests.
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NPavel Hrdina <phrdina@redhat.com>

src/conf/virinterfaceobj.c

@@ -182,7 +182,7 @@ virInterfaceObjListFindByMACStringCb(void *payload,
     virObjectLock(obj);
 
     if (STRCASEEQ(obj->def->mac, data->matchStr)) {
-        if (VIR_STRDUP(data->macs[data->nmacs], data->matchStr) < 0) {
+        if (VIR_STRDUP(data->macs[data->nmacs], obj->def->name) < 0) {
             data->error = true;
             goto cleanup;
         }