This cherry picks:
- b6fe0440c637 ("bridge: implement missing ndo_uninit()")
- b1b9d366028f ("bridge: move bridge multicast cleanup to ndo_uninit")
The fix is in b1b9d366028f ("bridge: move bridge multicast cleanup
to ndo_uninit") but it requires b6fe0440c637 ("bridge: implement missing
ndo_uninit()"). Furthermore, b1b9d366028f needed some manual resolution
of a cherry-pick conflict because the surrounding code had changed.
Signed-off-by: Rolf Neugebauer <rn@rneugeba.io>