rpvdev->notify is called from four places in this file: virtqueue
notify, set_status, set_features, and write_config. None guarded
against notify being NULL, valid when no mailbox is configured, and
none checked the returned status. Add a shared rpvdev_notify()
helper used at all four sites: skip when notify is NULL, log a
warning via metal_log on nonzero return. Exported notify signature
is unchanged, per discussion in issue #343.
Assisted-by: Claude <noreply@anthropic.com>
Signed-off-by: Atul Akella <atul.akella@gmail.com>
Document that callers must zero-initialize the endpoint structure
before calling rpmsg_create_ept, including the release_cb field.
Fixes#659
Signed-off-by: Atul Akella <atul.akella@gmail.com>