hostapd: Avoid unnecessary Beacon frame update for co-location

hostapd: Avoid unnecessary Beacon frame update for co-location

When it comes to set some BSS's beacon, there are two reasons to
update the beacon of co-located hostapd_iface(s) at the same time:
1. 6 GHz out-of-band discovery
2. MLD operational parameters update

BSS load update is unrelated with the above two reasons, and therefore
is not the case to update beacon for co-location. Moreover, updating
beacon for co-location when BSS load update makes hostapd set beacon too
frequently, which makes hostapd busy setting beacon in a multi-BSS case.

Add a new function to update beacon only for current BSS and use the
function during BSS load update.

Signed-off-by: Michael Lee <michael-cy.lee@mediatek.com>
Signed-off-by: Money Wang <money.wang@mediatek.com>