Set default timing and control ports in Dockerfile

[marecabo]

This change adds sed commands to the Dockerfile so the timing and control ports for Airplay are already set in the config file.

See https://github.com/Ulrar/hassio-addons/issues/9#issuecomment-643738054

These commands change

#airplay_shared {
        # UDP ports used when airplay devices make connections back to forked-daapd
        # (choosing specific ports may be helpful when running forked-daapd behind a firewall)
#       control_port = 0
#       timing_port = 0
#}

to

airplay_shared {
        # UDP ports used when airplay devices make connections back to forked-daapd
        # (choosing specific ports may be helpful when running forked-daapd behind a firewall)
        control_port = 3690
        timing_port = 3691
}

Side Question: Should we also change # type = "alsa" to type = "pulseaudio" already in the Dockerfile as mentioned here https://github.com/Ulrar/hassio-addons/issues/1#issuecomment-640094598 in a similar fashion?

[Ulrar]

Hi,

That's a good idea yes, alsa won't ever work in hassio so there's no point in leaving that in. Thanks !