I found Some problem on dtlsInfo initialzation

Our server use the licode to connect to openwebrtc but some problem will lead to some error
When create offer dtlsinfo will be undefined anytime ,because of a thread sync problem,
the dtlsInfo will be generated at bridgeServer.js but it can't actually get the value every time because the function is a async
so,we can use a callback function to confirm the callback at dtlsInfo initializtion then to generate the SDP .

Start in bridgeServer.js and trace the asynchronous dtlsInfo initialization used while creating an offer. Confirm where the value can be unavailable, then ensure SDP generation waits for initialization; done means create-offer no longer produces an undefined dtlsInfo error.

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