add compile time checks for MB_MASTER_TCP_ENABLED

Signed-off-by: AshUK <github.AshUK@outlook.com>

components/freemodbus/tcp_slave/modbus_controller/mbc_tcp_slave.c

@@ -28,6 +28,8 @@
 #include "mbc_tcp_slave.h"          // for tcp slave mb controller defines
 #include "port_tcp_slave.h"         // for tcp slave port defines
 
+#if MB_TCP_ENABLED
+
 // Shared pointer to interface structure
 static mb_slave_interface_t* mbs_interface_ptr = NULL;
 
@@ -221,3 +223,5 @@ esp_err_t mbc_tcp_slave_create(void** handler)
 
     return ESP_OK;
 }
+
+#endif //#if MB_TCP_ENABLED