modbus_tcp

add lwip_strerr
fix tcp_close

tests/mocs.h

@@ -120,7 +120,7 @@ void tcp_recv(void* pcb, tcp_recv_fn arg);
 void tcp_setprio(void* pcb, uint8_t prio);
 void tcp_err(void* pcb, void* err);
 void tcp_poll(void* pcb, void* poll, uint8_t interval);
-void tcp_close(void* pcb);
+err_t tcp_close(void* pcb);
 
 void tcp_write(void* pcb, const char* data, size_t len, uint8_t apiflags);
 void tcp_output(void* pcb);
@@ -131,6 +131,8 @@ size_t tcp_sndbuf(void* pcb);
 
 uint16_t pbuf_copy_partial(const struct pbuf* buf, void* dataptr, uint16_t len, uint16_t offset);
 
+const char* lwip_strerr(err_t err);
+
 #ifdef __cplusplus
 }
 #endif