a_iface: fix memory leaks

Fix multiple memory leaske in A/BSSMAP code

Change-Id: I90703c96e6a266a1cfa60b184139375aeb9ae32d
diff --git a/include/osmocom/msc/a_iface.h b/include/osmocom/msc/a_iface.h
index a49ede2..32003eb 100644
--- a/include/osmocom/msc/a_iface.h
+++ b/include/osmocom/msc/a_iface.h
@@ -51,7 +51,7 @@
 /* Initalize A interface connection between to MSC and BSC */
 int a_init(struct osmo_sccp_instance *sccp, struct gsm_network *network);
 
-/* Send DTAP message via A-interface */
+/* Send DTAP message via A-interface, take ownership of msg */
 int a_iface_tx_dtap(struct msgb *msg);
 
 /* Send Cipher mode command via A-interface */