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.
These wrappers allow a caller to provide UDPMux and TCPMux instances
to the ICE agent that represent multiple open ports. This can be
desirable in what would otherwise be single-port deployments, as it
increases the chance that one of the fixed ports will not be blocked
by a users firewall.
