TransportPolicy::Relay doesn't work

[bigfarts]

agent_add_candidate_pairs_for_remote in libjuice will add all candidates despite the TransportPolicy, including local ones. In TransportPolicy::Relay mode, agent_add_candidate_pairs_for_remote should add only relayed candidates and avoid adding any direct candidates.

[paullouisageneau]

This is libjuice-specific, I'm opening an issue in libjuice for this.