rename ipacc_connect_proxy_bind() to rsl_ipacc_mdcx_to_rtpsock()

Our RTP sockets are no longer just for the proxy mode, so having
"proxy" in the function name is really misleading.
diff --git a/openbsc/src/abis_rsl.c b/openbsc/src/abis_rsl.c
index 05735ee..a50d7aa 100644
--- a/openbsc/src/abis_rsl.c
+++ b/openbsc/src/abis_rsl.c
@@ -1615,6 +1615,20 @@
 	return abis_rsl_sendmsg(msg);
 }
 
+/* tell BTS to connect RTP stream to our local RTP socket */
+int rsl_ipacc_mdcx_to_rtpsock(struct gsm_lchan *lchan)
+{
+	struct rtp_socket *rs = lchan->abis_ip.rtp_socket;
+	int rc;
+
+	rc = rsl_ipacc_mdcx(lchan, ntohl(rs->rtp.sin_local.sin_addr.s_addr),
+				ntohs(rs->rtp.sin_local.sin_port),
+			/* FIXME: use RTP payload of bound socket, not BTS*/
+				lchan->abis_ip.rtp_payload2);
+
+	return rc;
+}
+
 int rsl_ipacc_pdch_activate(struct gsm_lchan *lchan)
 {
 	struct msgb *msg = rsl_msgb_alloc();