[bsc] Move the GSM 04.08 helper functions to gsm_04_08_utils.c

The existing gsm_04_08.c implementation is mixing BSC and MSC
behavior. Move some simple parsing and generation functions over
to gsm_04_08_utils.c to allow a different MSC to define the policy.
diff --git a/openbsc/src/Makefile.am b/openbsc/src/Makefile.am
index cd0a0e6..30968b0 100644
--- a/openbsc/src/Makefile.am
+++ b/openbsc/src/Makefile.am
@@ -5,16 +5,16 @@
 noinst_LIBRARIES = libbsc.a libmsc.a libvty.a
 noinst_HEADERS = vty/cardshell.h
 
-libbsc_a_SOURCES = abis_rsl.c abis_nm.c gsm_data.c \
+libbsc_a_SOURCES = abis_rsl.c abis_nm.c gsm_data.c gsm_04_08_utils.c \
 		msgb.c select.c chan_alloc.c timer.c debug.c \
-		gsm_subscriber_base.c subchan_demux.c bsc_rll.c \
+		gsm_subscriber_base.c subchan_demux.c bsc_rll.c transaction.c \
 		trau_frame.c trau_mux.c paging.c e1_config.c e1_input.c tlv_parser.c \
 		input/misdn.c input/ipaccess.c signal.c gsm_utils.c talloc.c \
 		talloc_ctx.c
 
 libmsc_a_SOURCES = gsm_subscriber.c db.c telnet_interface.c \
-		mncc.c rtp_proxy.c gsm_04_08.c gsm_04_11.c transaction.c token_auth.c \
-		rrlp.c
+		mncc.c rtp_proxy.c gsm_04_08.c gsm_04_11.c transaction.c \
+		token_auth.c rrlp.c
 
 libvty_a_SOURCES = vty/buffer.c vty/command.c vty/vector.c vty/vty.c