[sccp] Add a force_free method for connections

E.g. when the underlying connection transport medium is gone
one needs to force to close SCCP connections, add this helper.

It will remove the connection from the list of connections and
it will free the data.
diff --git a/openbsc/src/sccp/sccp.c b/openbsc/src/sccp/sccp.c
index 4bd87c8..e0fd02e 100644
--- a/openbsc/src/sccp/sccp.c
+++ b/openbsc/src/sccp/sccp.c
@@ -1198,6 +1198,17 @@
 	return 0;
 }
 
+int sccp_connection_force_free(struct sccp_connection *con)
+{
+	if (con->connection_state > SCCP_CONNECTION_STATE_NONE &&
+	    con->connection_state < SCCP_CONNECTION_STATE_RELEASE_COMPLETE)
+		llist_del(&con->list);
+
+	con->connection_state = SCCP_CONNECTION_STATE_REFUSED;
+	sccp_connection_free(con);
+        return 0;
+}
+
 struct sccp_connection *sccp_connection_socket(void)
 {
 	return talloc_zero(tall_sccp_ctx, struct sccp_connection);