virtio: uapi: Drop __packed attribute in linux/virtio_pci.h

virtio: uapi: Drop __packed attribute in linux/virtio_pci.h

Commit 92792ac752aa ("virtio-pci: Introduce admin command sending function")
added "__packed" structures to UAPI header linux/virtio_pci.h. This triggers
build failures in the consumer userspace applications without proper "definition"
of __packed (e.g., kvmtool build fails).

Moreover, the structures are already packed well, and doesn't need explicit
packing, similar to the rest of the structures in all virtio_* headers. Remove
the __packed attribute.

Fixes: 92792ac752aa ("virtio-pci: Introduce admin command sending function")
Cc: Feng Liu <feliu@nvidia.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Yishai Hadas <yishaih@nvidia.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
Reviewed-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Message-Id: <20240125232039.913606-1-suzuki.poulose@arm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>