Compile USE_IBVERBS & work with RoCEv2

[tianfengfrank]

Hi, we are trying to enable the ibverbs & make it work with RoCEv2 (e.g., using both librdma_cm & libibverbs). However, we cannot successfully compile the source code.

Our question is whether Gloo can work with RDMA (RoCEv2 instead of IPoIB or RoCEv1) now? Do we have any documentation for transport part (it shows 'TBD' in doc folder)? Thanks.

Extra Info: When we tried to build Gloo with USE_IBVERBs option, following error shows up: /home/tian/gloo/gloo/transport/ibverbs/device.h:22:2: error: #error "Expected GLOO_HAVE_TRANSPORT_IBVERBS to be defined"