nixos/home/routing-common: Working IPv6 router

lib/constants.nix

@@ -180,14 +180,17 @@ rec {
       hi = {
         v4 = subnet 4 1 all.v4;
         v6 = subnet 4 1 all.v6;
+        mtu = hiMTU;
       };
       lo = {
         v4 = subnet 3 1 all.v4;
         v6 = subnet 4 2 all.v6;
+        mtu = 1500;
       };
       untrusted = {
         v4 = subnet 6 16 all.v4;
         v6 = subnet 4 3 all.v6;
+        mtu = 1500;
       };
       inherit (colony.prefixes) as211024;
     };

lib/default.nix

@@ -4,7 +4,7 @@ let
   inherit (lib)
     genAttrs mapAttrsToList filterAttrsRecursive nameValuePair types
     mkOption mkOverride mkForce mkIf mergeEqualOption optional
-    showWarnings concatStringsSep flatten unique;
+    showWarnings concatStringsSep flatten unique optionalAttrs;
   inherit (lib.flake) defaultSystems;
 in
 rec {
@@ -152,6 +152,9 @@ rec {
       LLDP = true;
       EmitLLDP = "customer-bridge";
     };
+    linkConfig = optionalAttrs (a.mtu != null) {
+      MTUBytes = toString a.mtu;
+    };
     ipv6AcceptRAConfig = {
       Token = mkIf (a.ipv6.iid != null) "static:${a.ipv6.iid}";
       UseDNS = true;