client: use bigger TTL, expose it to clients

This value is better be known to users and it's better be more than two since
we can have more complicated communications in future.

Refs. nspcc-dev/neofs-node#2447

Signed-off-by: Roman Khimov <roman@nspcc.ru>

client/common.go

@@ -16,6 +16,10 @@ const (
 	fieldNumSigPubKey = 1
 	fieldNumSigVal    = 2
 	fieldNumSigScheme = 3
+
+	// DefaultTTL is a TTL used for NeoFS requests if no other value is
+	// set specifically for a call.
+	DefaultTTL = 8
 )
 
 // groups meta parameters shared between all Client operations.
@@ -120,7 +124,7 @@ func (x contextCall) prepareRequest() {
 	}
 
 	if meta.GetTTL() == 0 {
-		meta.SetTTL(2)
+		meta.SetTTL(DefaultTTL)
 	}
 
 	if meta.GetVersion() == nil {
@@ -137,7 +141,7 @@ func (x contextCall) prepareRequest() {
 func (c *Client) prepareRequest(req request, meta *v2session.RequestMetaHeader) {
 	ttl := meta.GetTTL()
 	if ttl == 0 {
-		ttl = 2
+		ttl = DefaultTTL
 	}
 
 	verV2 := meta.GetVersion()