bsc: Prepare to have multiple MSC connections

We now have a list of MSCs but in the code we will
try to access the MSC with the nr 0.
diff --git a/openbsc/src/osmo-bsc/osmo_bsc_sccp.c b/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
index 6ac3007..cc4eedf 100644
--- a/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
+++ b/openbsc/src/osmo-bsc/osmo_bsc_sccp.c
@@ -195,7 +195,12 @@
 	struct sccp_connection *sccp;
 
 	net = conn->bts->network;
-	msc = &net->bsc_data->msc;
+	msc = osmo_msc_data_find(net, 0);
+	if (!msc) {
+		LOGP(DMSC, LOGL_ERROR, "Failed to select a MSC.\n");
+		return -1;
+	}
+
 	if (!msc->msc_con->is_authenticated) {
 		LOGP(DMSC, LOGL_ERROR, "Not connected to a MSC. Not forwarding data.\n");
 		return -1;