drivers/apc_modbus.c: report (in debug traces) whether USB-capable li…

…bmodbus was used to build this driver [networkupstools#2666]

Signed-off-by: Jim Klimov <[email protected]>

drivers/apc_modbus.c

@@ -1579,8 +1579,10 @@ void upsdrv_makevartable(void)
 #endif /* defined NUT_MODBUS_HAS_USB */
 
 #if defined NUT_MODBUS_HAS_USB
+	upsdebugx(1, "This build of the driver is USB-capable; also Serial and TCP Modbus RTU are supported");
 	addvar(VAR_VALUE, "porttype", "Modbus port type (serial, tcp, usb, default=usb)");
 #else
+	upsdebugx(1, "This build of the driver is not USB-capable, only Serial and TCP Modbus RTU are supported");
 	addvar(VAR_VALUE, "porttype", "Modbus port type (serial, tcp, default=serial)");
 #endif /* defined NUT_MODBUS_HAS_USB */
 	addvar(VAR_VALUE, "slaveid", "Modbus slave id (default=1)");