when both rpl_semi_sync_MASTER,SLAVE_enabled set the server should recover as master

When at recovery both rpl_semi_sync_MASTER,SLAVE_enabled variables are set ON
the server recovers as a semisync slave to conduct binlog truncation according to MDEV-21117.

While which of the roles the user means with the settings is unclear, and considering that switchover must be of lesser demand compare to a "normal" master crash-recovery, a presumed intent is better off be for MASTER.

That is when both variables are ON a post-crash restarting server would execute the normal recovery.