[subscr] Split gsm_subscriber.c in BSC and MSC part

For the BSC part we still assign a gsm_subscriber to lchan but it
might only contain the TMSI of this subscriber.

For the MSC part we will need the HLR/VLR feature of the gsm_subscriber,
specially the lookup's by number...

So if libbsc.a/libmsc.a are compiled in one app and used the
subscribers will be shared, and if only libbsc.a gets used we will
have more empty gsm_subscriber.c..
diff --git a/openbsc/tests/db/Makefile.am b/openbsc/tests/db/Makefile.am
index fbd9b9b..c8a3970 100644
--- a/openbsc/tests/db/Makefile.am
+++ b/openbsc/tests/db/Makefile.am
@@ -4,5 +4,5 @@
 noinst_PROGRAMS = db_test
 
 db_test_SOURCES = db_test.c
-db_test_LDADD = $(top_builddir)/src/libmsc.a $(top_builddir)/src/libbsc.a -ldl -ldbi
+db_test_LDADD = $(top_builddir)/src/libbsc.a $(top_builddir)/src/libmsc.a -ldl -ldbi