ACS: Fix not selecting the best channel in the segment

ACS: Fix not selecting the best channel in the segment

Fix the following bugs about selecting the best channels in the segment:
1. If the 'update_best' once became false, it never becomes true again.
   In other word, if one of the channels in the segment is not usable,
   the remaining channels in the segment were never able to be the best
   channel.
2. The primary channel in the segment might not be usable due to the
   insufficient survey data. Therefore, it cannot be the best channel and
   we cannot take its factor/weight into account.

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