During ieee80211_set_active_links() we do (among the others):
1. Call drv_change_vif_links() with both old_active and new_active
2. Unassign the chanctx for the removed link(s) (if any)
3. Assign chanctx to the added link(s) (if any)
4. Call drv_change_vif_links() with the new_active links bitmap

The problem here is that during step #1 the driver doesn't know whether
we will activate multiple links simultaneously or are just doing a link
switch, so it can't check there if multiple links are supported/enabled.
(Some of the drivers might enable/disable this option dynamically)

And during step #3, in which the driver already knows that,
returning an error code (for example when multiple links are not
supported or disabled), will cause a warning, and we will still complete
the transition to the new_active links.
(It is hard to undo things in that stage, since we released channels etc.)

Therefore add a driver callback to check if the desired new_active links
will be supported by the driver or not. This callback will be called
in the beginning of ieee80211_set_active_links() so we won't do anything
before we are sure it is supported.
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Reviewed-by: Gregory Greenman <gregory.greenman@intel.com>
Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Link: https://msgid.link/20231220133549.64c4d70b33b8.I79708619be76b8ecd4ef3975205b8f903e24a2cd@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>