[ofiwg] completion flags as actually defined by OFI

[Hefty, Sean]

> > I believe the providers support this guarantee.
> 
> Including the clean shutdown case?

For FI_TRANSMIT_COMPLETE:

- The sockets and psm providers do not generate a completion until the remote side has processed the request and acknowledged the data.
- Cisco needs to confirm the usnic provider behavior, but it's UD anyway.  I believe it adheres to the description given for completions on unreliable endpoints.
-  Verbs does not generate a completion until the data has been acked by the remote side, unless I'm remembering it wrong.

It seems reasonable to assume that a message that has been acked will complete successfully at the peer.