The AMR transmission phase directly depends on the frame number. The
transmission phase is used to tell if a received AMR frame contains a
CMI (frame type that is currently used) or CMR (frame type that the
receiver should use) codec identifier. The formulas in the present
implementation seem to be correct but they do not reflect the numbers in
the spec very well, nor do they have unit-tests. Lets replace them with
more readble functions and test those functions with unit-tests.
Change-Id: I94a934a6b3b397b4cd0e9da3577325de58814335
Related: SYS#5549