Drivers: hv: vmbus: On write cleanup the logic to interrupt the host

Drivers: hv: vmbus: On write cleanup the logic to interrupt the host

BugLink: http://bugs.launchpad.net/bugs/1661430
Signal the host when we determine the host is to be signaled.
The currrent code determines the need to signal in the ringbuffer
code and actually issues the signal elsewhere. This can result
in the host viewing this interrupt as spurious since the host may also
poll the channel. Make the necessary adjustments.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 1f6ee4e7d83586c8b10bd4f2f4346353d04ce884)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Marcelo Cerri <marcelo.cerri@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>