libfabric: update embedded libfabric to 934a714

Update the embedded copy of libfabric to the github ofiwg/libfabric
repo hash 934a714ca85f1a30a1e384a7d5f714ee962dc253.
libfabric: Open MPI addition to stem a flood of warnings

Add a pragma to not warn about zero-length arrays.  This needs to be
addressed upstream, but for now, do it here.
usnic: update for libfabric API change

Use FI_ADDR_UNSPEC for posting a receive from an unspecified source.