bts: fix osmo-bts.cfg: change osmux local-ip 127.0.0.{1->11}

When running ttcn3-bts-test natively (without Docker), the osmux
related testcases TC_speech_osmux_tch[fh] fail because both osmo-bts
and the testsuite are configured to bind() at '127.0.0.1:1984'.

Change-Id: I768933c83ae9dd2cd65eed955b2f823b6421cc4c

bts/osmo-bts.cfg

@@ -64,7 +64,7 @@ bts 0
  pcu-socket /tmp/pcu_sock
  osmux
   use on
-  local-ip 127.0.0.1
+  local-ip 127.0.0.11
   local-port 1984
  trx 0
   power-ramp max-initial 0 mdBm