xen/9pfs: send responses back to the frontend

xen/9pfs: send responses back to the frontend

Once a request is completed, xen_9pfs_push_and_notify gets called. In
xen_9pfs_push_and_notify, update the indexes (data has already been
copied to the sg by the common code) and send a notification to the
frontend.

Schedule the bottom-half to check if we already have any other requests
pending.

Signed-off-by: Stefano Stabellini <[email protected]>
CC: [email protected]
CC: [email protected]
CC: Aneesh Kumar K.V <[email protected]>
CC: Greg Kurz <[email protected]>