l3cfg: fix pruning of ACD data
Summary
Resubmit patch ed565f91 from !1734 (merged), that was reverted because it was causing a crash.
The crash was caused by unconditionally clearing acd_data_pruning_needed
in _l3cfg_update_combined_config()
, which leaded to an inconsistent state.
The flag needs to be cleared only when actually committing the configuration.
Edited by Beniamino Galvani