WebRTC: Support vhost or domain.

[wukaMM]

Description

1. SRS version(Version): 4.0
2. SRS log is as follows(Log):

[2020-06-24 08:49:35.706][Warn][23882][715][11] RTC disabled in vhost 
[2020-06-24 08:49:35.706][Warn][23882][715][11] RTC error code=5021 : Disabled server=1, rtc=0, vhost=
thread [23882][715]: do_serve_http() [src/app/srs_app_http_api.cpp:942][errno=11]
[2020-06-24 08:49:36.396][Warn][23882][715][104] client disconnect peer. ret=1007

1. SRS configuration is as follows(Config):

rtc_server {
    enabled         on;
    # Listen at udp://8000
    listen          8008;
    #
    # The $CANDIDATE means fetch from env, if not configed, use * as default.
    #
    # The * means retrieving server IP automatically, from all network interfaces,
    # @see https://github.com/ossrs/srs/issues/307#issuecomment-599028124
    candidate       $CANDIDATE;
}

vhost us-east.faster.im {
    rtc {
        enabled     on;
        bframe      discard;
    }
}

Replay

When using defaultVhost in vhost, playback has no problem.
But webrtc://us-east.faster.im/live/2470505512036576660 is invalid in rtc player, Got answer 400

Expect

Hope to use the domain name for playback.