bhyve: keep physical and virtual COMMAND reg in sync

[corvink]

Summary

On startup all virtual BARs are registered. Additionally, the encoding bit in the virtual cmd register is set. After that, the passthru emulation overwrites the virtual cmd register with the physical one. This could lead to a mismatch between registered BARs and the encoding bits in the cmd register. Instead of writing the physical to the virtual cmd register, write the virtual to the physical cmd register to solve this issue.

[manu]

LGMT.
Will commit next monday unless someone have more comments until then.