BTS_Tests: decouple payload generation from f_rtpem_activate()

This function is going to be used by the upcoming testcases for CSD
specific channel modes.  Generating the Rx/Tx payload(s) now becomes
the duty of the calling function.  So far the only user of this API
is f_TC_speech_rtp(), so move the speech payload generation there.

Change-Id: I9e823c33b1dbbadd57bc63df25b8ddf368d76232
Related: OS#1572
1 file changed