debug first ambe frame
support system image version letters other than 'S'
Revert "debug first ambe frame"

This reverts commit a5f5ae5961d5eae64f82ad5c07ce072a8dbe1df9.
version number experiment
serial ports now use DMA instead of interrupts
send voice+data packets exactly every 20ms to network or phy
fixed buffer overflow bug; sending lots of data (e.g. PHY update) now works
new snmp variable for version information
only write to LCD if screen content changes
preliminary hotspot function
preliminary hotspot function
Merge branch 'dl1bff_master' of github.com:dl1bff/up4dar-os into dl1bff_master
check LCD periodically and reset if necessary
fixed ipv4 address can now be configured via snmp
remote display via snmp
DM mode can now be selected
several bugs fixed
send only valid frames to reflector
autostart in all modes
code for pressing the buttons over snmp