webrtcbin: use regular ice nomination by default

  1. We don't currently deal with an a=ice-options in the SDP which means we currently violate https://tools.ietf.org/html/rfc5245#section-8.1.1 which states: "If its peer is using ICE options (present in an ice-options attribute from the peer) that the agent does not understand, the agent MUST use a regular nomination algorithm."
  2. The recommendation is default to regular nomination in both RFC5245 and RFC8445. libnice change for this is libnice/libnice!125 which requires an API break in libnice.

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