avahi-daemon service: Add option to enable point-to-point interfaces.

nixos/modules/services/networking/avahi-daemon.nix

@@ -21,6 +21,7 @@ let
     use-ipv6=${if ipv6 then "yes" else "no"}
     ${optionalString (interfaces!=null) "allow-interfaces=${concatStringsSep "," interfaces}"}
     ${optionalString (domainName!=null) "domain-name=${domainName}"}
+    allow-point-to-point=${if allowPointToPoint then "yes" else "no"}
 
     [wide-area]
     enable-wide-area=${if wideArea then "yes" else "no"}
@@ -98,6 +99,15 @@ in
         '';
       };
 
+      allowPointToPoint = mkOption {
+        default = false;
+        description= ''
+          Whether to use POINTTOPOINT interfaces. Might make mDNS unreliable due to usually large
+          latencies with such links and opens a potential security hole by allowing mDNS access from Internet
+          connections. Use with care and YMMV!
+        '';
+      };
+
       wideArea = mkOption {
         default = true;
         description = ''Whether to enable wide-area service discovery.'';