[Flexradio] Digi mode ops beware of MIC GAIN setting

[Ken N9VV]

Digi mode ops: beware of MIC GAIN setting. It is 
defaulted to 50 which severely overdrives using
my previous LINE OUT settings for MixW and 1.3.12.
I found that a setting of < 30 gives IMD < 28,
but MIC GAIN settings > 30 quickly drop IMD to -17db 
(using external KK7UQ IMD monitor).
de Ken N9VV