Automatic disable LAN DHCP when WAN is unavilable

[EngineerSB]

We use Netgate in our mobile units. When we goto site the client provides an eithernet connection and this gets plugged into the WAN and everything works as normal.

The system plugged up as follows.

3 x AP's > Netgate Lan, Netgate Wan > Client Internet

Some clients have the meshing system and we do at the office to and when this is available the AP will connect to the Mesh and serve internet that way. So we need a means to detect if the physical WAN is connected and if not disbale DHCP on the Netgate so it doesnt try and manage the network.