ssb: Before destroying a connection, show a message on why it is going away in the UI.

src/ssb.h

@@ -1093,6 +1093,13 @@ void tf_ssb_connection_adjust_read_backpressure(tf_ssb_connection_t* connection,
 */
 void tf_ssb_connection_adjust_write_count(tf_ssb_connection_t* connection, int delta);
 
+/**
+** Get the reason why a connection is going away.
+** @param connection The connection.
+** @return The reason or NULL.
+*/
+const char* tf_ssb_connection_get_destroy_reason(tf_ssb_connection_t* connection);
+
 /**
 ** Initiate a tunnel connection.
 ** @param ssb The SSB instance.