In #475, import low-level API (ReadMsgUDP) to determine
destination interface for packets received by UDPConn listen
at any(unspecified) address, to fix msg received by incorrect
candidate that shared same ufrags. But the api has compatibility
issues, also not reliable in some special network cases like
AWS/ECS.
So this pr revert that change, and make UDPMuxDefault not
accept Conn listen at unspecified address. Also provide a
NewMultiUDPMuxFromPort helper function to create a MultiUDPMux
to listen at all addresses.
For ice gather, it will use UDPMux's listen address to generate
canidates instead of create it from interfaces.
When we have multiple host candidates and mux to a
single port, if these candidates share a same conn
(either tcp or udp), they might read other's msg
cause ice connection cost long time or failed.
UDPMux before only worked with UDP4 traffic.
UDP6 traffic would simply be ignored.
This commit implements 2 connections per ufrag. When requesting a
connection for a ufrag the user must specify if they want IPv4 or IPv6.
Relates to pion/webrtc#1915
The original UDPMux only works for the HOST candidates.
UniversalUDPMux adds support for SRFLX candidates
and will later support Relay candidates.
UniversalUDPMux embeds UDPMuxDefault and
handles STUN server packets to discover XORMappedAddr
forwarding the remaining packets for muxing to UDPMuxDefault.
