rename more items from nitb to bsc

A NITB is a BSC + MSC, and if a BTS talks to a NITB, it talks to the BSC part
of the NITB. Hence it makes more sense to name certain things 'bsc' instead of
'nitb', to prepare for a separate BSC process appearing soon.

Change-Id: I6a0343b9243b166d4053cc44f523543f1245d772
diff --git a/example/defaults.conf b/example/defaults.conf
index 3685446..b1e26f0 100644
--- a/example/defaults.conf
+++ b/example/defaults.conf
@@ -7,7 +7,7 @@
     auth_policy: closed
     encryption: a5 0
 
-nitb_bts:
+bsc_bts:
   location_area_code: 23
   base_station_id_code: 63
   stream_id: 255