Fix interactive exec over TLS

The code no longer assumes a net.TCPConn underlying the HTTP connection
in order to close attached streams.

Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>
Removed race condition
If two interrupts were fired really quickly interruptCount could have been incremented twice before the LoadUint32 making cleanup not being called at all.

Signed-off-by: Erik Dubbelboer <erik@dubbelboer.com>
Merge pull request #9543 from ErikDubbelboer/racefix

Removed race condition
Merge pull request #9497 from icecrime/86580-tls_interactive_exec

Fix interactive exec over TLS