More clever RTP transport remote address switch

[bennylp]

Currently the UDP and ICE media transport has the capability to switch destination RTP/RTCP address to the source address of the RTP/RTCP packets, if they are different than the original address set in SDP received from remote.

It may be better to put this functionality in the stream instead, for the following reason:

• the stream has more information about the packet, such as RTP pt, SSRC, and info from RTCP statistic
• some application that uses media transport wants to inspect and possibly filter the source address
• some firewall wants us to send the RTP to the address in SDP, regardless of the source address of the RTP packet