Failed to set remote answer sdp: Called in wrong state: stable

(sdp_offer_answer.cc:761): 
Failed to set remote answer sdp: Called in wrong state: stable
 OnFailure INVALID_STATE: 
 Failed to set remote answer sdp: Called in wrong state: stable

当第二次得到远端的sdp answer并尝试设置时报错如上，经测试解决方法如下，需要在Conductor类里添加如下函数：

void Conductor::DeletePeerConnection(