SDAP: close TUN socket to unblock thread and clean interface shutdown

* Close entity->pdusession_sock manually before pthread_join() to unblock sdap_tun_read_thread()
* Update tun_destroy() to open a fresh socket for interface management, independent from the data socket
* Fix check on success of change_interface_state() in tun_destroy(): is a boolean
* Handle ENODEV error when bringing interface down: treat as success if the interface is already gone.
* tun_destroy() is now handling INTERFACE_DOWN, so `INTERFACE_DOWN` in `tun_config()` is no longer needed

common/utils/tun_if.h

@@ -84,8 +84,7 @@ int tun_alloc(const char *dev);
 /*!
  * \brief This function destroys the TUN interface
  * \param[in] dev name of the interface
- * \param[in] fd file descriptor of the allocated interface
  */
-void tun_destroy(const char *dev, int fd);
+void tun_destroy(const char *dev);
 
 #endif /*TUN_IF_H_*/