nat: Create a method to determine if any MSC is connected.

In the future we will have multiple MSC connections so we will
need to figure if any of them is active.
diff --git a/openbsc/include/openbsc/bsc_nat.h b/openbsc/include/openbsc/bsc_nat.h
index c5a9258..11d1f23 100644
--- a/openbsc/include/openbsc/bsc_nat.h
+++ b/openbsc/include/openbsc/bsc_nat.h
@@ -338,4 +338,6 @@
 
 struct bsc_nat_acc_lst_entry *bsc_nat_acc_lst_entry_create(struct bsc_nat_acc_lst *);
 
+int bsc_nat_msc_is_connected(struct bsc_nat *nat);
+
 #endif
diff --git a/openbsc/src/nat/bsc_nat.c b/openbsc/src/nat/bsc_nat.c
index 7c4a03d..ef3f9a9 100644
--- a/openbsc/src/nat/bsc_nat.c
+++ b/openbsc/src/nat/bsc_nat.c
@@ -883,7 +883,7 @@
 	/*
 	 * if we are not connected to a msc... just close the socket
 	 */
-	if (!nat->msc_con->is_connected) {
+	if (!bsc_nat_msc_is_connected(nat)) {
 		LOGP(DNAT, LOGL_NOTICE, "Disconnecting BSC due lack of MSC connection.\n");
 		close(fd);
 		return 0;
diff --git a/openbsc/src/nat/bsc_nat_utils.c b/openbsc/src/nat/bsc_nat_utils.c
index a96cd01..39de817 100644
--- a/openbsc/src/nat/bsc_nat_utils.c
+++ b/openbsc/src/nat/bsc_nat_utils.c
@@ -23,6 +23,7 @@
  */
 
 #include <openbsc/bsc_nat.h>
+#include <openbsc/bsc_msc.h>
 #include <openbsc/gsm_data.h>
 #include <openbsc/debug.h>
 #include <openbsc/ipaccess.h>
@@ -508,3 +509,8 @@
 	llist_add_tail(&entry->list, &lst->fltr_list);
 	return entry;
 }
+
+int bsc_nat_msc_is_connected(struct bsc_nat *nat)
+{
+	return nat->msc_con->is_connected;
+}