Some fixes and TEST of firmware

NEW: Added caching of packets before sending to increase ethernet performance.
FIX: Removed all testing serial link output to increase sniffing performance.

Firmware fully tested on board V20, on CAN bus at 500kbps, with 48% load.
IP address changed back to unicast because of work on heavy-load ethernet bus.
SYNC frame transmission dropped because of frame already used in the testing scenario.

Sniffed without packet drops.

Bugs found in the firmware:
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 - No bugs revealed in firmware.

Bugs found in the GUI:
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 * long-term viewing of packet log slows down app.