Whilst fixing issues with SSDP on devices with multiple interfaces, i came across a design issue in the current code - namely interfaces without a gateway were ignored.

Removing this also removed the attempt to detect virtual interfaces - so i implemented a work around solution (see 4 below) to keep the functionality.

Whilst in the area, I also fixed a few minor bugs i encountered (1, 5, 6 below) and stopped SSDP messages from going out on non-LAN interfaces (3)

All these changes are related.

Changes

1. IsInPrivateAddressSpace - improved subnet code checking
2. interfaces with no gateway were being excluded from SSDP blasts
3. filtered SSDP blasts from not LAN addresses as defined on the network page.
4. removed Backmerge submodule updating strategy jellyfin/jellyfin#986 mod - as this was part of the issue of SSDP blasts and listen are on 'default' interface, needs to be smart or configurable jellyfin/jellyfin#2986. Interfaces can be excluded from the LAN by putting the LAN address in brackets. eg. [10.1.1.1] will exclude an interface with ip address 10.1.1.1 from SSDP
5. fixed a problem where an invalid LAN address causing the SSDP to crash
6. corrected local link filter (FilterIPAddress) to filter on 169.254. addresses