Fix "SCTP failed" if no DataChannel is created on a Transport with enableSctp: true

[ibc]

Details

• Fixes If a Transport is created with enableSctp: true and no DataChannel is created, after ~4 minutes it emits sctpstatechange with state "failed" #1748
• Bonus: Don't even try to start DTLS handshake if ICE is not yet connected/completed.

[ibc]

Some comments before I enter into details:

• "transport connected" doesn't mean that transport.connect() was called. In a WebRtcTransport it means that DTLS is connected. In a PlanTransport it is always true from the beginning. Please see in Transport.cpp and WebRtcTransport.cpp when TransportConnected() is called.
• We need "sctpDataReceived" because the transport may receive SCTP data (INIT chunk) before the DataProducer/Consumer request arrives to the worker (typical race condition between signaling and media) so we optimize it as follows: if SCTP data is received it means that the peer has enabled DataChannel so we allow such a received INIT chunk and start connecting our side. Otherwise the received SCTP INIT chunk could be ignored, so peer would resend it after some time etc.