libmsc: struct smsc: drop 'const' qualifier from bind_addr

This pointer holds an address of a string allocated on heap.

Change-Id: I50145b57494aaccd4793f7b0ed2f65a6641db929
Related: CID#240711
diff --git a/src/libmsc/smpp_smsc.h b/src/libmsc/smpp_smsc.h
index b26d011..4c0d701 100644
--- a/src/libmsc/smpp_smsc.h
+++ b/src/libmsc/smpp_smsc.h
@@ -110,7 +110,7 @@
 	struct llist_head esme_list;
 	struct llist_head acl_list;
 	struct llist_head route_list;
-	const char *bind_addr;
+	char *bind_addr;
 	uint16_t listen_port;
 	char system_id[SMPP_SYS_ID_LEN+1];
 	int accept_all;