MDEV-28879 Assertion `l->lsn <= log_sys.get_lsn()' failed around recv_recover_page

recv_recover_page(): Correct a debug assertion to refer to recv_sys.lsn,
which may be ahead of log_sys.lsn during non-final recovery batches.
In commit 685d958e (MDEV-14425)
when some redundant LSN fields were removed,
log_sys.log.scanned_lsn had been replaced with a reference to
log_sys.lsn instead of the more appropriate recv_sys.lsn.

recv_scan_log(): Remove a redundant call to log_sys.set_recovered_lsn().
It suffices to adjust the log_sys.lsn after parsing (and before starting
to apply) records for the last batch.

Note: Normally, log_sys.lsn must be the latest log sequence number.
Before the final recovery batch, this may be safely violated, because
log_write_up_to() will be a no-op. That function will be invoked by the
buf_flush_page_cleaner thread to initiate writes of recovered pages.

storage/innobase/log/log0recv.cc

@@ -2918,7 +2918,7 @@ static buf_block_t *recv_recover_page(buf_block_t *block, mtr_t &mtr,
 		const log_phys_t* l = static_cast<const log_phys_t*>(recv);
 		ut_ad(l->lsn);
 		ut_ad(end_lsn <= l->lsn);
-		ut_ad(l->lsn <= log_sys.get_lsn());
+		ut_ad(l->lsn <= recv_sys.lsn);
 
 		ut_ad(l->start_lsn);
 		ut_ad(recv_start_lsn <= l->start_lsn);
@@ -3561,13 +3561,11 @@ void recv_sys_t::apply(bool last_batch)
 
   if (last_batch && srv_operation != SRV_OPERATION_RESTORE &&
       srv_operation != SRV_OPERATION_RESTORE_EXPORT)
+    /* Instead of flushing, last_batch sorts the buf_pool.flush_list
+    in ascending order of buf_page_t::oldest_modification. */
     log_sort_flush_list();
   else
-  {
-    /* Instead of flushing, last_batch could sort the buf_pool.flush_list
-    in ascending order of buf_page_t::oldest_modification. */
     buf_flush_sync_batch(lsn);
-  }
 
   if (!last_batch)
   {
@@ -3738,7 +3736,6 @@ static bool recv_scan_log(bool last_phase)
         else
         {
           ut_ad(store == STORE_IF_EXISTS);
-          log_sys.set_recovered_lsn(recv_sys.lsn);
           recv_sys.apply(false);
         }
       }