xen/events/fifo: reset control block and local HEADs on resume

xen/events/fifo: reset control block and local HEADs on resume

commit c12784c3d14a2110468ec4d1383f60cfd2665576 upstream.

When using the FIFO-based event channel ABI, if the control block or
the local HEADs are not reset after resuming the guest may see stale
HEAD values and will fail to traverse the FIFO correctly.

This may prevent one or more VCPUs from receiving any events following
a resume.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>