use osmo_sockaddr_str_is_nonzero()

Also regard an RTP port as invalid if the IP address is 0.0.0.0.
Achieve this by using osmo_sockaddr_str_is_nonzero() instead of
osmo_sockaddr_str_is_set().

Depends: I73cbcab90cffcdc9a5f8d5281c57c1f87b2c3550 (libosmocore)
Change-Id: I53ddb19a70fda3deb906464e1b89c12d9b4c7cbd
diff --git a/src/libmsc/msc_t.c b/src/libmsc/msc_t.c
index 6b96c26..af0ddaa 100644
--- a/src/libmsc/msc_t.c
+++ b/src/libmsc/msc_t.c
@@ -444,7 +444,7 @@
 
 	/* Also need to fetch the RTP IP:port from AoIP Transport Address IE to tell the MGW about it */
 	if (rtp_ran) {
-		if (osmo_sockaddr_str_is_set(&r->remote_rtp)) {
+		if (osmo_sockaddr_str_is_nonzero(&r->remote_rtp)) {
 			LOG_MSC_T(msc_t, LOGL_DEBUG, "From Handover Request Ack, got " OSMO_SOCKADDR_STR_FMT "\n",
 				  OSMO_SOCKADDR_STR_FMT_ARGS(&r->remote_rtp));
 			rtp_stream_set_remote_addr(rtp_ran, &r->remote_rtp);