enable USB tethering

related links:

• Manjarno & Phosh request - phosh#77
• PP & Debian (Manjarno mentioned) - https://forum.pine64.org/showthread.php?tid=10723&pid=73888#pid73888
• I can confirm - the anx7688 module has no effect - https://gitlab.com/mobian1/issues/-/issues/57
• usb_gadget_setup.sh works for me (post. I used it without modification, but .. 😉)
• creating a connection e.g. nmcli con add type ethernet con-name usbTethering ifname usb0 ipv4.method shared (article)