DLEP peer not up when router supports less extension than modem

[weihuang72]

One Dlep run as router, doesn't support latency extension.
One Dlep run as modem, supports latency extension.
The modem when it sends back session initialization response, it still includes data item 65411 (latency range) which is defined in latency extension. This makes the router throw error and the peer is not up.