[dpdk-stable] [PATCH v2] net/ixgbe: fix probability of obtaining mailbox lock failure

[Qiming Chen]

This is a problem triggered by the existing network. I discovered it a long time ago. I use the link state as an example. 
It is not to say that it is a link state problem, but to show that ixgbevf does have such a probability problem. 
The current modification and repeated verification can indeed solve the problem. The specific root cause of the problem may not be analyzed. 
Since the mailbox itself has a reliability mechanism, why not use it here?I understand that the status of the vf mailbox is read from the register. 
If you repeatedly reset the pf, will the transient fail because the register value has not been initialized, and it will succeed later?