BSC CBSP: apply changes to 'cbc' vty section, switch server<->client modes

With Icaa2775cc20a99227dabe38a775ff808b374cf98, osmo-bsc no longer allows
configuring CBSP as both server and client at the same time, and the 'cbc' VTY
section has a different structure.

Adjust the 'cbc' section in osmo-bsc.cfg.

For each CBSP test init, switch osmo-bsc's CBSP link to server or client mode
by new vty command 'cbc' / 'mode (server|client|disabled)'.

Related: Icaa2775cc20a99227dabe38a775ff808b374cf98 (osmo-bsc)
Related: I9e9760121265b3661f1c179610e975cf7a0873f1 (docker-playground)
Related: OS#4702
Change-Id: I7eea0dd39de50ed80af79e0f10c836b8685d8644
diff --git a/bsc/osmo-bsc.cfg b/bsc/osmo-bsc.cfg
index f8be2cd..8dd6655 100644
--- a/bsc/osmo-bsc.cfg
+++ b/bsc/osmo-bsc.cfg
@@ -424,6 +424,10 @@
 ctrl
  bind 127.0.0.1
 cbc
- remote-ip 127.0.0.1
- remote-port 48049
- listen-port 48050
+ mode disabled
+ client
+  remote-ip 127.0.0.1
+  remote-port 48049
+ server
+  local-ip 127.0.0.1
+  local-port 48050