Don't set tlsext_host_name for NonBlockingHTTPBOSH, because it has no _owner

NonBlockingHTTPBOSH instance has no attribute _owner and therefor the Server
of the _owner cannot be set as tlsext_host_name. This should fix #8911. Maybe
additional work is needed to make HTTPBOSH work with XEP-0368.
Status Job ID Name Coverage
  Test
failed #3983
run-test

failed #3711
run-test

 
  Build
skipped #3712
run-build
 
Name Stage Failure
failed
run-test Test There has been a timeout failure or the job got stuck. Check your timeout limits or try again
No job trace