wifi: mac80211: run NAN DE code only when appropriate

wifi: mac80211: run NAN DE code only when appropriate

NAN DE (Discovery Engine) may be handled in the device or in user space.
When handled in user space, all the NAN func management code should not
run. Moreover, devices with user space DE should not provide the
add/del_nan_func callbaks. For such devices, ieee80211_reconfig_nan will
always fail.

Make it clear what parts of ieee80211_if_nan are relevant to DE
management, and touch those only when DE is offloaded.

Add a check that makes sure that a driver doesn't register with
add_del/nan_func callbacks if DE is in user space.

Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20260326121156.6665f64865cd.Iee24bef3bae2e1d502216192e760c1e699d271c9@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>