rtp: Move the RTP Proxy code out of RSL into the BSC/MSC domain

Instead of creating the sockets in the RSL code we will do this
in the CRCX_ACK, MDCX_ACK, DLCX_IND signal handler of gsm_04_08.
Introduce a handover signal so we can repatch the RTP sockets in
the gsm_04_08 as well.
diff --git a/openbsc/src/Makefile.am b/openbsc/src/Makefile.am
index cc69a72..c86fc26 100644
--- a/openbsc/src/Makefile.am
+++ b/openbsc/src/Makefile.am
@@ -22,7 +22,7 @@
 		trau_frame.c trau_mux.c paging.c e1_config.c e1_input.c \
 		input/misdn.c input/ipaccess.c handover_logic.c \
 		talloc_ctx.c system_information.c rest_octets.c \
-		rtp_proxy.c bts_siemens_bs11.c bts_ipaccess_nanobts.c \
+		bts_siemens_bs11.c bts_ipaccess_nanobts.c \
 		bts_unknown.c bsc_version.c bsc_api.c bsc_vty.c meas_rep.c gsm_04_80.c
 
 libmsc_a_SOURCES = gsm_subscriber.c db.c \
@@ -30,7 +30,7 @@
 		gsm_04_08.c gsm_04_11.c transaction.c \
 		token_auth.c rrlp.c ussd.c silent_call.c \
 		handover_decision.c auth.c \
-		osmo_msc.c
+		osmo_msc.c rtp_proxy.c
 
 libvty_a_SOURCES = common_vty.c