webrtc_js: Fix incorrect casing in trickle ICE TCP candidate
Make also the related port be 9 for non-host TCP active candidates

In accordance with RFC 6544
peerhandler: Use the correct property name to enable/disable FIR
Don't create the RTCP component and elements when multiplexing RTP/RTCP

Also clarify the description of the rtcp-mux property

Closes #41