Changes

pcuif: fix TXT_IND/PCU_VERSION BTS initialization behavior

The PCU sends a TXT_IND with the PCU_VERSION as first message after
the socket connection is established. The BTS uses those messages
to trigger some initialization (allocate BTS object inside the
PCU, send SI to the PCU).

Unfortunately the PCU will send the TXT_IND with the PCU_VERSION
always with to BTS 0. The 0 in this case is a hardcoded fake BTS
number (There is no BTS object allocated under this number in the
PCU at this point). The BTS will then do the initialization process
for BTS 0, which is only correct by chance since osmo-bts currently
only supports one BTS object with the number 0. Nevertheless it is
incorrect to use the BTS number from the TXT_IND to resolve the BTS
object.

Let's fix this design error by introducing a broadcast BTS number,
we then send the TXT_IND with the PCU_VERSION to that broadcast
BTS number. The BTS will then do the initialization for all BTS
objects it is aware of (BTS 0)

Related: OS#6507
Change-Id: I5316d3b7cef416eb19bb256f4ccc1468b3efe1c6
Depends: osmo-bsc.git Ie92f5833a80b06e78c6cec8f03f054e2e2625fad
Depends: osmo-pcu.git Id01966a1ee52d0f5e465dc2e0eaf85e5b7942f81
Depends: osmo-ttcn3-hacks.git Idce13d55fc5bdbf5b366e3a60d9b46aacfc701a9
Depends: docker-playground.git I15f7150b51047379a557a1f8df6330eca597f2e3