IB/rdmavt: Use kzalloc_node

Use kzalloc_node instead of kzalloc for rdmavt memory region segment
allocation to optimize for performance on NUMA platforms.

Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>