nts: close file after loading cookies

Don't forget to close the file with cookies in ntsdumpdir if
successfully loaded.

Fixes: 2fa83b541c ("nts: save and load cookies on client")

nts_ntp_client.c

@@ -669,6 +669,8 @@ load_cookies(NNC_Instance inst)
   inst->last_nke_success = context_time + SCH_GetLastEventMonoTime();
   inst->context_id = context_id;
 
+  fclose(f);
+
   DEBUG_LOG("Loaded %d cookies for %s", i, filename);
   return;