BTS_Tests.ttcn: fix: use reasonable minimum default for C/I

Since [1] we additionally filter Access Bursts by the link quality
(defined by C/I) in L1SAP, and since [2] we do provide the actual
C/I values for osmo-bts-trx, as was received from the transceiver.

[1] https://gerrit.osmocom.org/r/I893ec9c6c2ebad71ea68b2dc5f9f5094dfc43b78
[2] https://gerrit.osmocom.org/r/I8d86dec7ebc039cbfd038c4342ff328b11281865

The default minimum C/I for Access Bursts in OsmoBTS is 50 cB,
while the TTCN-3 test cases configure fake_trx.py to send 0 cB,
so all Access Bursts are getting dropped, as expected.

Let's use 60 cB (or 6 dB) by default. This change makes Access
Bursts pass again, and thus fixes some broken test cases.

Change-Id: Ic345f7995c2553e346590cd851f8857d26e7beb2
1 file changed