GFSK is used by many low cost unlicensed transceivers chips, such as Si44xx, SX1231, CC11xx, ADF70xx, etc.
This
patch is made from gmsk.py, but allows FM sensitivity to be changed
independently to permit wider FM deviations used by these radio chips.
The intention is to not touch/break GMSK (for GSM users), but instead add gfsk.py.
MSK has fixed 0.25 modulation index, where FSK can have modulation indexes usually between 0.5 and 2.0
This is tested using example gfsk_loopback.grc, based off of dpsk_loopback example.