IuUP: allow Initialization from any address if not yet set

Do not refuse IuUP Initialization messages coming in on an RTP port if
the remote IP address is not yet known.
If an IUFP conn is not yet configured (pre-Initialization), allow rx
from any remote address if the remote IP address is not yet known.

If we refuse the IuUP Initialization, a 3G RNC may fail to set up a RAB.
We will know the remote address only *after* assigning a RAB succeeded.
So the IuUP Initialization must be allowed before knowing all addresses.

At the time of writing, CRCX for IUFP are sent to osmo-mgw in either
LOOPBACK or in RECVONLY mode:
- current osmo-msc: recvonly
- osmo-msc <= v1.10.0: loopback
- osmo-hnbgw: loopback
IuUP Initialization should work regardless of that.
See also next patch I158dd046fdfcb10392cde3de8cc88dd095a05b40

IuUP is one layer below the loopback/send/recv decision for RTP; IuUP is
always terminated at the MGW, while the AMR payload carries through.

Related: alternative patch Idd833997abce46886e9664505b2776fa5dadc8db
Related: SYS#6657
Change-Id: I6c365559a7bd197349f0ea99f7a13b56a4bb580b

src/libosmo-mgcp/mgcp_network.c

@@ -835,6 +835,18 @@ static int check_rtp_origin(struct mgcp_conn_rtp *conn, struct osmo_sockaddr *ad
 	char ipbuf[INET6_ADDRSTRLEN];
 
 	if (osmo_sockaddr_is_any(&conn->end.addr) != 0) {
+		if (mgcp_conn_rtp_is_iuup(conn) && !conn->iuup.configured) {
+			/* Allow IuUP Initialization to get through even if we don't have a remote address set yet.
+			 * This is needed because hNodeB doesn't announce its IuUP remote IP addr to the MGCP client
+			 * (RAB Assignment Response at HNBGW) until it has gone through IuUP Initialization against
+			 * this MGW here. Hence the MGW may not yet know the remote IuUP address and port at the time
+			 * of receiving IuUP Initialization from the hNodeB.
+			 */
+			LOGPCONN(conn->conn, DRTP, LOGL_INFO,
+				 "Rx RTP from %s: allowing unknown src for IuUP Initialization\n",
+				 osmo_sockaddr_to_str(addr));
+			return 0;
+		}
 		switch (conn->conn->mode) {
 		case MGCP_CONN_LOOPBACK:
 			/* HACK: for IuUP, we want to reply with an IuUP Initialization ACK upon the first RTP