This adds a check for the previous SYS_AUTOSTART id. If it is still the
old/previous SYS_AUTOSTART id, it will flash the new bootloader as well
as set the proper SYS_AUTOSTART id.
- no longer start sercon or mavlink usb by default
- on USB connection (VBUS) monitor serial USB at low rate and start Mavlink if there's a HEARTBEAT or nshterm on 3 consecutive carriage returns
- the mavlink USB instance is automatically stopped and serdis executed if USB is disconnected
- skipping Mavlink USB (and sercon) saves a considerable amount of memory on older boards
Julian Oes