Modify the client side non-application data record upcall so that it is
done via a kthread.

There was a glitch in the upcall handling without this patch, in that
the upcall was done by a thread doing an RPC.
The problem with this was that there might not be an RPC done for
minutes, hours,...
This patch changes the code so that a kthread runs for each client
side TLS connection and does the upcalls.