ivshmem: add missing msix calls

ivshmem: add missing msix calls

ivshmem used msix but didn't call it on either reset or
config write paths. This used to partically work since
guests don't use all of msi-x configuration fields,
and reset is rarely used, but the patch 'msix: track function masked
in pci device state' broke that. Fix by adding appropriate calls.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reported-by: Cam Macdonell <cam@cs.ualberta.ca>
Tested-by: Cam Macdonell <cam@cs.ualberta.ca>