This implements RTP based GSM BER testing for osmo-bts, implementing
ideas described in https://osmocom.org/projects/osmobts/wiki/BER_Testing
In short: The command transmits a PRBS sequence encapsulated in RTP
frames, which are sent to the BTS, which transmits that data in the
(unimpaired) downlink. The mobile station receives the data and is
instructed to loop it back in the (possibly impaired) uplink. The BTS
receives that uplink, puts in in RTP frames which end up being received
back by this very tool. By correlating the received RTP with the PRBS
sequence, this tool can compute the BER (Bit Error Rate) of the
(possibly impaired) uplink. Doing this with different RF channel model
simulators in the uplink allows to establish BER at different levels and
channel conditions.
Original code by Sylvain Munaut extended with some comments and Automake
integration by Harald Welte.
Change-Id: I1cffa0ae959e29ec61775b13185fd1057ed7485a