Class C tested for EU_868

[novvere]

Low datarate optimization on AGC auto on for DR11 and DR12, otherwise CRC_ERROR is detected by RFM in CLASS C continuos mode.
Other minor changes.

[novvere]

Tested with ChirpStack, TTN Madrid V7 board with ABP and OTAA. As this board is still in development I will try testing with V2 board based on Arduino Nano 328P

[sabas1080]

Wow, good look for me. @wero1414

[novvere]

Tested in ATMega 328P using TTN MAdrid v2 node (https://github.com/IoTopenTech/Nodo_TTN_MAD_V2_2)
On ARM micros just using 'const' puts constants in Flash memory but AVR needs PROGMEM macro. I added PROGMEM to be compatible with both microprocessors.

[novvere]

Some of the problems I found testing Class C where related to the regional parameters, frequencies and data rates even working with TTN. I can only test with EU_868 so, if something goes wrong in other regions, activate DEBUG and check values sent to FRM just before going continuous receive to see if it meets correct freq and data rate.

[mattjbailey]

I have not seen a good example of a working class C code yet. The default settings for this code are US915, yet no working examples for this band. Am I missing something? I have searched and searched with no luck.