In libfabric v1.0.0 (i.e., API v1.0), the usnic provider handled
FI_MSG_PREFIX inconsistently between sends and receives. This has
been fixed in libfabric v1.1.0 (i.e., API v1.1): FI_MSG_PREFIX is
handled consistently for both sends and receives.
Run-time detect which libfabric we are running with and adapt behavior
appropriately.