networking: Disable resolvconf

Fixes an issue where newer versions of the Mullvad module would cause
websites to not resolve.

See: https://discourse.nixos.org/t/connected-to-mullvadvpn-but-no-internet-connection/35803

modules/networking.nix

@@ -12,6 +12,8 @@
 
     useHostResolvConf = true;
 
+    resolvconf.enable = false;
+
     nat = {
       enable = true;
       internalInterfaces = [ "ve-+" ];