Fix tethering on Android N (Nougat)

First you need to have a rooted phone, then use adb shell or a terminal emulator and paste this:

content insert --uri content://settings/global --bind name:s:tether_dun_required \
  --bind value:i:0

Without root, from your pc you could try

adb shell settings put global tether_dun_required 0

Done.