ICE media transport should have a default option to switch RTP transmission to source address if remote doesn't use ICE

[bennylp]

When local endpoint is configured with ICE, and when remote doesn't use ICE, the ICE media transport should be able to switch the RTP transmission to the source address of the RTP packets, just like the usual UDP media transport.

This is to support the case when remote is using private IP address (e.g. STUN is not enabled), or when remote is behind a symmetric NAT.