nixos/home: Prefer dave for stream RSTP

Set explicit port costs so `stream` prefers `dave` over `jim`.

Trigger `mstpd` when the bridge is configured, before it is routable.

docs/sites/home/stream.md

@@ -76,8 +76,9 @@ box sets:
 ## Switching (RSTP)
 
 `stream` is dual-homed to both switches: `lan-jim` (igc) and `lan-dave` (mlx4_en), both MTU 9000,
-are enslaved to the `lan` bridge with `STP=true`. [`routing-common/mstpd.nix`](../../../nixos/boxes/home/routing-common/mstpd.nix)
+are enslaved to the `lan` bridge with `STP=true`. The explicit bridge-port costs prefer
-runs a patched `mstpd` and forces RSTP on `lan` once it's routable, so exactly one uplink carries
+`lan-dave` at 10 over `lan-jim` at 100. [`routing-common/mstpd.nix`](../../../nixos/boxes/home/routing-common/mstpd.nix)
+runs a patched `mstpd` and forces RSTP on `lan` once it is configured, so exactly one uplink carries
 traffic at a time. (The remaining NICs are renamed `et2`/`et5` and left unconfigured.)
 
 ## Deployment

nixos/boxes/home/routing-common/mstpd.nix

@@ -24,7 +24,7 @@ in
   services = {
     networkd-dispatcher.rules = {
       configure-mstpd = {
-        onState = [ "routable" ];
+        onState = [ "configured" ];
         script = ''
           #!${pkgs.runtimeShell}
           if [ "$IFACE" = "lan" ]; then

nixos/boxes/home/stream.nix

@@ -115,10 +115,7 @@
                 Name = "lan";
                 Kind = "bridge";
               };
-              extraConfig = ''
+              bridgeConfig.STP = true;
-                [Bridge]
-                STP=true
-              '';
             };
           };
           links = {
@@ -175,10 +172,12 @@
             "50-lan-jim" = {
               matchConfig.Name = "lan-jim";
               networkConfig.Bridge = "lan";
+              bridgeConfig.Cost = 100;
             };
             "50-lan-dave" = {
               matchConfig.Name = "lan-dave";
               networkConfig.Bridge = "lan";
+              bridgeConfig.Cost = 10;
             };
 
             "50-wan-ifb" = {