Add untagged access ports and a staging uplink for gw-cnx-1

New cnx.router.accessPorts option pins a port untagged to one VLAN via
bridge PVID/EgressUntagged; convention is the last copper port as an
always-available mgmt recovery port. gw-cnx-1 port roles: enp1s0 WAN,
enp2s0 trunk, enp3s0 temporary DHCP uplink into the old OPNsense LAN
(back to trunk at cutover), enp4s0 untagged mgmt.

modules/router/default.nix

@@ -160,6 +160,19 @@ in
       description = "LAN ports carrying all VLANs tagged (incl. any 10G SFP+ ports).";
     };
 
+    accessPorts = lib.mkOption {
+      type = lib.types.attrsOf lib.types.str;
+      default = { };
+      example = {
+        enp4s0 = "mgmt";
+      };
+      description = ''
+        Ports acting as untagged access ports on a single VLAN (port name ->
+        VLAN name). Frames are untagged on the wire; the bridge tags them with
+        the VLAN's PVID. Use for an always-available on-site mgmt port.
+      '';
+    };
+
     vlans = lib.mkOption {
       type = lib.types.attrsOf (lib.types.submodule vlanModule);
       description = "VLANs served at this site; `mgmt` and `lan` are mandatory.";
@@ -172,6 +185,14 @@ in
         assertion = cfg.vlans ? mgmt && cfg.vlans ? lan;
         message = "cnx.router: every site must define the `mgmt` and `lan` VLANs.";
       }
+      {
+        assertion = lib.all (v: cfg.vlans ? ${v}) (lib.attrValues cfg.accessPorts);
+        message = "cnx.router: every accessPorts value must name a defined VLAN.";
+      }
+      {
+        assertion = lib.all (p: !(cfg.accessPorts ? ${p})) cfg.trunkPorts;
+        message = "cnx.router: a port cannot be both a trunk and an access port.";
+      }
     ];
 
     # Router diagnostics toolkit: packets (tcpdump), path (mtr), link
@@ -270,6 +291,21 @@ in
           };
         }) cfg.trunkPorts
       )
+      // lib.mapAttrs' (
+        port: vlanName:
+        lib.nameValuePair "25-access-${port}" {
+          matchConfig.Name = port;
+          networkConfig.Bridge = "br0";
+          bridgeVLANs = [
+            {
+              VLAN = cfg.vlans.${vlanName}.id;
+              PVID = cfg.vlans.${vlanName}.id;
+              EgressUntagged = cfg.vlans.${vlanName}.id;
+            }
+          ];
+          linkConfig.RequiredForOnline = "no";
+        }
+      ) cfg.accessPorts
       // lib.mapAttrs' (
         name: vlan:
         lib.nameValuePair "40-${vlanIf name}" {