[Help needed] Why is cfg80211 missing symbols on load? (with mt76, on MT7688)

I can't get my LEDE build for the Omega2 (MT7688 based) working with WiFi with current LEDE master any more (worked in October).

At startup, cfg80211 can't load because it cannot resolve some symbols:

[   39.180715] cfg80211: Unknown symbol bp_extack_genl_unregister_family (err 0)
[   39.189235] cfg80211: Unknown symbol bp_extack_genl_register_family (err 0)

As a consequence, everything depending on it (mac80211, mt76, mt7603e, mt76x2e) cannot load and the system comes up with no WiFi.

It is probably something really stupid, but I can't find it. The symbol name bp_extack_genl_unregister_family seems to indicate that it has to do something with libnl and extack, and possibly related to recent kernel patches in that area (here and here), but understanding this is still above my head.

The same configuration built and worked fine back at October 19th with LEDE 9887afb1af.

To make absolutely sure this is not due to stale build problems in my normal working tree, I created a 100% fresh LEDE tree and just applied the diffconfig and ran a complete build. Result is exactly the same.
[Update: In the meantime I also checked my diffconfig against the default config for the Omega2 target, and there are no relevant differences (my config leaves away a lot of userland stuff I don't need and adds some packages from my own feed, but does not change anything in the network stack config)]

Any help or hints what to check are welcome, I really am running out of ideas (and expertise) about how to track this down :frowning:
Thanks in advance!