USB tethering broken in 6.15 with some phones

We're told by users about this regression vs. 6.14.2 which worked fine.

Reports

• wb:e41028e7e87af067f07dc528e22a4597
  • Xiaomi Redmi 10C
  • wwan0 is created, successful MAC spoof
  • ModemManager[5443]: [base-manager] couldn't check support for device '/sys/devices/pci0000:00/0000:00:1c.4/0000:04:00.0/usb1/1-1': not supported by any plugin
• wb:823e412c13fcb9fa0a6f801debf3a60c
  • Fairphone 4 5G
  • wwan0 is created, successful MAC spoof
• Another report tells us USB tethering still works with an older phone, but is broken with a new one.

Workaround for users

Use the phone as a Wi-Fi hotspot. This may use more battery.