Changes

bsc CBSP: fix osmo-bsc.cfg to contain 3 BTS with a CBCH

The bsc/BSC_Tests_CBSP.ttcn rely on a configuration where the first three BTS
carry out SMSCB messaging, and the fourth BTS does not. That requires a CBCH
channel config on bts 0, 1, 2.

Related: Iac46ee2cc5bc0978d5f5baa550baf493a7c56b1b (osmo-ttcn3-hacks)
Change-Id: Idbcc703ace7012fb395f0eef3e445df28b368d74