GTP tunnel enhancements

GTP is enhanced to update the GTP tunnel and session lifetime to avoid GTP tunnel timeout issues. Even if the GTP-U validation is disabled, the GTP-U traffic can refresh the GTP tunnel to avoid timeout. Only GTPv1 and GTPv2 tunnels, not GTPv0 tunnels, are refreshed by the GTP-U traffic. Before refreshing the GTP tunnel, you must enable the GTP-U distribution. The GTP-U tunnel has a session attach flag that is checked when scanning the GTP-U tunnels. If the session attach flag is present in the tunnel, the timer will not decrease and prevents the tunnel from being deleted while the tunnel is still in service.