Drivers: hv: vmbus: Check for pending channel interrupts before taking a CPU offline

Check that enough time has passed such that the modify channel message
has been processed before taking a CPU offline.

Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210416143449.16185-4-parri.andrea@gmail.com


Signed-off-by: Wei Liu <wei.liu@kernel.org>