UAVOFrSkySPortBridge: fixed absence of byte stuffing
UAVOFrSKYSPortBridge: ignore_rx_chars reflects real count of transmitted bytes
UAVOFrSKYSPortBridge: added comment regarding tx buffer size
UAVOFrSKYSPortBridge: added comment regarding checksum calculation
Merge pull request #1340 from xdandys/smartport_fix

FrSky SmartPort bugfix