Remove bottleneck in validation (#923)

Even with debugLibrary not enabled ValueStr is calculated in this call,
which causes significant bottlenecks in validation.

All other calls to DbgPrint already use ValueStrDebug to avoid formatting
string output that won't ever be used.

ytypes/validate.go

@@ -96,7 +96,7 @@ func Validate(schema *yang.Entry, value interface{}, opts ...ygot.ValidationOpti
 		}
 	}
 
-	util.DbgPrint("Validate with value %v, type %T, schema name %s", util.ValueStr(value), value, schema.Name)
+	util.DbgPrint("Validate with value %v, type %T, schema name %s", util.ValueStrDebug(value), value, schema.Name)
 
 	switch {
 	case schema.IsLeaf():