Commit fada4ac3 introduced the usage of kthread API.
kthread_stop is a blocking function which returns only when
the thread exits. In this case, the thread can't exit because it's
waiting for the write lock, which is being held by cmtp_del_connection()
which is waiting for the thread to exit -- deadlock.

Revert cmtp_reset_ctr to its original behavior: non-blocking signalling
for the session to terminate.
Signed-off-by: NPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: NGustavo F. Padovan <padovan@profusion.mobi>