nixos/ollama: update port option, use types.port

nixos/modules/services/misc/ollama.nix

@@ -78,11 +78,11 @@ in
         '';
       };
       port = lib.mkOption {
-        type = types.nullOr types.ints.u16;
+        type = types.port;
         default = 11434;
         example = 11111;
         description = ''
-          Which port the ollama server listens to. Set to `null` to not specify a port.
+          Which port the ollama server listens to.
         '';
       };
       acceleration = lib.mkOption {
@@ -135,11 +135,7 @@ in
       environment = cfg.environmentVariables // {
         HOME = cfg.home;
         OLLAMA_MODELS = cfg.models;
-        OLLAMA_HOST =
-          if cfg.port == null then
-            cfg.host
-          else
-            "${cfg.host}:${toString cfg.port}";
+        OLLAMA_HOST = "${cfg.host}:${toString cfg.port}";
       };
       serviceConfig = {
         ExecStart = "${lib.getExe ollamaPackage} serve";