[virtio] Ensure that device is closed before unmapping regions
Commit 988243c ("[virtio] Add virtio-net 1.0 support") erroneously
placed the code to unmap the device regions before the code to
unregister the network device. In the common case that the network
device is still open at the time that we shut down to boot the OS,
this results in the regions being accessed after having been unmapped.
For 32-bit BIOS or for UEFI with no IOMMU enabled, the iounmap()
operation is a no-op and so the driver still happens to work despite
the ordering bug. For 64-bit BIOS or for UEFI with an IOMMU enabled,
the iounmap() operation is not a no-op, and the driver will trigger a
page fault.
Fix by moving the call to unregister_netdev() to before the code that
unmaps the device regions.
Signed-off-by: Michael Brown <mcb30@ipxe.org>
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