cfg: rework box_check_replication_synchro_quorum

Currently the box_check_replication_synchro_quorum helper
test for "replication_synchro_quorum" value being valid
and returns the value itself to use later in code.

This is fine for regular numbers but since we're gonna
support formula evaluation the real value to use will
be dynamic and returning a number "to use" won't be
convenient.

Thus lets change the context: make
box_check_replication_synchro_quorum() to return 0|-1
for success|failure and when the real value is needed
we will fetch it explicitly via cfg_geti call.

To make this more explicit the real update of the
appropriate variable is done via
box_update_replication_synchro_quorum() helper.

Part-of #5446

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>

src/box/box.cc

@@ -565,7 +565,7 @@ box_check_replication_synchro_quorum(void)
 			 "maximal number of replicas");
 		return -1;
 	}
-	return quorum;
+	return 0;
 }
 
 static double
@@ -766,7 +766,7 @@ box_check_config(void)
 	box_check_replication_connect_timeout();
 	box_check_replication_connect_quorum();
 	box_check_replication_sync_lag();
-	if (box_check_replication_synchro_quorum() < 0)
+	if (box_check_replication_synchro_quorum() != 0)
 		diag_raise();
 	if (box_check_replication_synchro_timeout() < 0)
 		diag_raise();
@@ -911,15 +911,22 @@ box_set_replication_sync_lag(void)
 	replication_sync_lag = box_check_replication_sync_lag();
 }
 
+void
+box_update_replication_synchro_quorum(void)
+{
+	int quorum = cfg_geti("replication_synchro_quorum");
+
+	replication_synchro_quorum = quorum;
+	txn_limbo_on_parameters_change(&txn_limbo);
+	box_raft_update_election_quorum();
+}
+
 int
 box_set_replication_synchro_quorum(void)
 {
-	int value = box_check_replication_synchro_quorum();
-	if (value < 0)
+	if (box_check_replication_synchro_quorum() != 0)
 		return -1;
-	replication_synchro_quorum = value;
-	txn_limbo_on_parameters_change(&txn_limbo);
-	box_raft_update_election_quorum();
+	box_update_replication_synchro_quorum();
 	return 0;
 }
 

src/box/box.h

@@ -251,6 +251,7 @@ void box_set_replication_timeout(void);
 void box_set_replication_connect_timeout(void);
 void box_set_replication_connect_quorum(void);
 void box_set_replication_sync_lag(void);
+void box_update_replication_synchro_quorum(void);
 int box_set_replication_synchro_quorum(void);
 int box_set_replication_synchro_timeout(void);
 void box_set_replication_sync_timeout(void);