Drivers: hv: vmbus: Prevent sending data on a rescinded channel

Drivers: hv: vmbus: Prevent sending data on a rescinded channel

BugLink: http://bugs.launchpad.net/bugs/1676635
After the channel is rescinded, the host does not read from the rescinded channel.
Fail writes to a channel that has already been rescinded. If we permit writes on a
rescinded channel, since the host will not respond we will have situations where
we will be unable to unload vmbus drivers that cannot have any outstanding requests
to the host at the point they are unoaded.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit e7e97dd8b77ee7366f2f8c70a033bf5fa05ec2e0)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>