Ignoring all unknown controls is not a good idea. 

Since not all OpenSSL versions and variants support "BIO_CTRL_POP" and "BIO_CTRL_PUSH", the following is change is a more proper patch.

This was tested with Tcl 8.6.13, tcltls-1.7.22 and OpenSSL 3.1.3 (19 Sep 2023).


````
--- tlsBIO.c-orig	2023-10-21 17:38:57
+++ tlsBIO.c	2023-10-22 11:32:02
@@ -278,7 +278,15 @@
 			dprintf("Got BIO_CTRL_FLUSH");
 			ret = ((Tcl_WriteRaw(chan, "", 0) >= 0) ? 1 : -1);
 			dprintf("BIO_CTRL_FLUSH returning value %li", ret);
+			break;
+#ifdef BIO_CTRL_POP
+                case BIO_CTRL_POP:
+                        dprintf("Got BIO_CTRL_POP");
+                        break;
+                case BIO_CTRL_PUSH:
+                        dprintf("Got BIO_CTRL_PUSH");
 			break;
+#endif
 		default:
 			dprintf("Got unknown control command (%i)", cmd);
 			ret = -2;
````