It is possible that the vmbus pcib channel is revoked during attach path.
The attach path could be waiting for response from host and this response will never
arrive since the channel has already been revoked from host point of view. Check
this situation during wait complete and return failed if this happens.
Reported by: Netapp
MFC after: 2 weeks
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D26486
75c2786c25