[ interfaces openvpn vtun0 ]
device vtun0 is already a member of a bridge; can't enslave it to bridge br0.
Error adding interface vtun0 to bridge br0

+bridge br0 {
+}
+openvpn vtun0 {
+    bridge-group {
+        bridge br0
+        cost 100
+    }
+    local-port 1234
+    mode site-to-site
+    protocol udp
+    remote-host 1.1.1.1
+    remote-port 1234
+    shared-secret-key-file /config/auth/foo
+}

[ interfaces openvpn vtun0 ]
set path cost failed: Numerical result out of range
Error setting bridge cost for vtun0