Connectivity is choppy when connected over a fast ETH WAN and a weak signal modem

## Test
Connect over Ethernet backhaul with a fast connection (I used 100mbps).
Insert a SIM under low signal strength conditions (I had 1 or 2 bars).
Try a video call or watch a video, there are a lot of drop outs.

Remove the SIM and reboot
Try a video call or watch a video, the experience is a lot better.

## Expected
Using multiple forms of backhaul, where one of them has a strong connection with high bandwidth, the user experience should be strong regardless of the quality of the other connections.

No files or tests are named. Reproduce the Ethernet-plus-low-signal-SIM scenario, then locate the Lua entry points handling WAN backhaul selection and modem connectivity; compare traffic behavior with and without the SIM. Done means video calls and playback remain stable over the strong Ethernet connection despite the weak modem signal.

Written by the indexing model from the issue text.