Merge branch 'ets-use-old-nbands-while-purging-unused-classes'

Davide Caratti says:

====================
ets: use old 'nbands' while purging unused classes

- patch 1/2 fixes a NULL dereference in the control path of sch_ets qdisc
- patch 2/2 extends kselftests to verify effectiveness of the above fix
====================

Link: https://patch.msgid.link/cover.1755016081.git.dcaratti@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>