The function can be used to send a VMbus packet and retrieve the
corresponding transaction ID.  It will be used by hv_pci.

No functional change.
Suggested-by: NMichael Kelley <mikelley@microsoft.com>
Signed-off-by: NAndrea Parri (Microsoft) <parri.andrea@gmail.com>
Reviewed-by: NMichael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220419122325.10078-4-parri.andrea@gmail.comSigned-off-by: NWei Liu <wei.liu@kernel.org>