OFI: Target CNTR with FI_WRITE only MRs

[jdinan]

Problem

OFI only allows catching FI_WRITE events on CNTRs bound to an MR. However, SOS enables both FI_WRITE and FI_READ on the MR, causing some providers to be unable to support the CNTR.

Solution

Add support for separate FI_WRITE and FI_READ MRs and enable the target CNTR only on the FI_WRITE MR.