Discovery set port option

I would like the option to specify which port the discovery module uses for the ssdp request it sends out. At the moment it gets any available port however this means it changes each time so I cannot ensure this port is open on my firewall. It would also be good to have discovery run one ssdp request for all devices and then make the output available to the various discovery sub-modules, at present each device type that implements discovery must do its own ssdp request on the network.