doc: Avoid duplicate rdma notes.

Change-Id: I5ede0ffad3870d8d86cb5d551ce188c649b04b44
Signed-off-by: Humble Chirammal <hchiramm@redhat.com>
Reviewed-on: http://review.gluster.org/8826
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>