CommsUDPSerialConnect multicast to allow address reuse

[magicrub]

When sending to a multicast port, such as 234.2.3.1:6969 for TAK, other apps on the same computer can't use that same multicast IP. Example: using WinTAK to test TAK messages from Mission Planner. There's an option in WinTAK networking settings to allow this, but for Mission Planner I think it's fine to always allow it

[magicrub]

This is the checkbox in WinTAK to enable this

[magicrub]

I'd also like to suggest having an option to ALWAYS do this, with a checkbox in the Config->Planner page.