osd/PeeringState: do not exclude up from acting_recovery_backfill

osd/PeeringState: do not exclude up from acting_recovery_backfill

If we choose a primary that does not belong to the current up set,
and all up peers are still recoverable, then we might end up excluding
some up peer from the acting_recovery_backfill set too due to the
"want size <= pool size" constraint (since https://github.com/ceph/ceph/pull/24035),
as a result of which all up peers might not get recovered in one go.

Fix by falling through any oversized want set to async recovery, which
should be able to handle it nicely.

Fixes: https://tracker.ceph.com/issues/42577
Signed-off-by: xie xingguo <xie.xingguo@zte.com.cn>