[misc] Move rtp_proxy.c into the libbsc.c

For the time being RSL has to know about Layer4 and upwards
and is using the RTP socket class....
diff --git a/openbsc/src/Makefile.am b/openbsc/src/Makefile.am
index f36a701..4def2e9 100644
--- a/openbsc/src/Makefile.am
+++ b/openbsc/src/Makefile.am
@@ -12,10 +12,10 @@
 		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 system_information.c bitvec.c rest_octets.c \
-		handover_decision.c meas_rep.c
+		handover_decision.c meas_rep.c rtp_proxy.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 \
+		mncc.c gsm_04_08.c gsm_04_11.c transaction.c \
 		token_auth.c rrlp.c gsm_04_80.c ussd.c silent_call.c
 
 libvty_a_SOURCES = vty/buffer.c vty/command.c vty/vector.c vty/vty.c