Implement connection_for_subscr() from a completely different angle: instead of
looking up lchans in bts structs, look up the subscriber in the global list of
gsm_subscriber_connection. static lchan_find() is thus obsoleted.
All callers of connection_for_subscr() live in libmsc, so move to libmsc.
The move and edit are done in a single commit since the old and new
implementation have nothing in common.
Future: osmo-cscn will use this, without bts being present.
Remove implementation of connection_for_subscr() from channel_test.c -- it is
possible that the abort() in there was intended for a regression test, but
actually it seems the implementation was merely added for linking reasons, and
the abort() added to guard against the NULL return value: no comment nor the
commit log indicate that the abort() is test critical; the addition was the
only change in channel_test.c for that commit; at the same time a
connection_for_subscr() call was added in libmsc.
Change-Id: I5e0ba0ecf1726ebd540800f4e98fdfc937c904ff
Neels Hofmeyr
1a60644eb2