Drivers: hv: vmbus: Handle channel rescind message correctly

Properly cleanup the channel state on receipt of the "offer rescind" message.
Starting with ws2012, the host requires that the channel "relid" be properly
cleaned up when the offer is rescinded.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>