bsc: change encryption a5 via VTY where needed

Do not assume that osmo-bsc.cfg contains "0 1 3 4" for master and "0 1 3"
for latest anymore. An upcoming test will need to change the value as
the test runs and needs a defined value to reset to.

Assume that osmo-bsc.cfg contains "0 1 3" and change it to "0 1 3 4"
only for TC_ciph_mode_a5_4.

Related: OS#4975
Related: docker-playground I55135ca00ef51de5cf6eaec75cfc20c21beef665
Change-Id: I3cf36c6ef86a0db050507f3737f4b0c10dcd52ed
diff --git a/bsc/osmo-bsc.cfg b/bsc/osmo-bsc.cfg
index 7b0fa2a..b64a63d 100644
--- a/bsc/osmo-bsc.cfg
+++ b/bsc/osmo-bsc.cfg
@@ -69,7 +69,7 @@
 network
  network country code 1
  mobile network code 1
- encryption a5 0 1 3 4
+ encryption a5 0 1 3
  neci 1
  paging any use tch 0
  handover 1