[OMPI devel] PML check for direct modex reviews needed (5.0 blocker)

[Zhang, William via devel]

Hello,

We need reviews for https://github.com/open-mpi/ompi/pull/7582 which is a 5.0 
blocker. Particularly, @artpol84 @karasevb please review this. We need to 
ensure it doesn't break the UCX PML.

Thanks,
William Zhang