rdma_reg_msgs is used to register an array of data buffers
that will be used send and/or receive messages on a queue pair associated with
an rdma_cm_id. The memory buffer is registered with the proteection
domain associated with the idenfier. The start of the data buffer array
is specified through the addr parameter, and the total size of the array
is given by length.
All data buffers should be registered before being posted as a work request.
Users must deregister all registered memory by calling rdma_dereg_mr.