Backport of fix for #1021

Note: The order of an if-statement matters if a variable isn't
declared. ;-)

Probably this 2.9.5 can live without it but rather play safe
and clean...

testssl.sh

@@ -13086,6 +13086,7 @@ initialize_globals() {
      do_tls_sockets=false
      do_client_simulation=false
      do_display_only=false
+     do_starttls=true
 }