mb master, slave add custom fc handlers

Kconfig

@@ -224,4 +224,21 @@ menu "Modbus configuration"
                 otherwise the only legacy types are supported. The extended types include
                 integer, float, double types with different endianness and size.
 
+    config FMB_CONTROLLER_SLAVE_ID_MAX_SIZE
+        int "Modbus Slave ID maximum buffer size (bytes)"
+        range 4 255
+        default 32
+        depends on FMB_CONTROLLER_SLAVE_ID_SUPPORT
+        help
+                Modbus slave ID buffer size used to store vendor specific ID information
+                for the <Report Slave ID> command.
+
+    config FMB_FUNC_HANDLERS_MAX
+        int "Maximum number of Modbus function handlers"
+        range 16 64
+        default 16
+        help
+                This option defines the maximum number of Modbus command handlers for Modbus master and slave.
+                The option can be useful to register additional commands and its handlers.
+
 endmenu