RDMA IO engine

RDMA IO engine

I have hacked an rdma ioengine based on OFED for fio which could test
both rdma memory semantic (rdma_write/rdma_read) and channel semantic
(send/recv). Would you like to merge this engine into fio?

notes
1) RDMA engine works in IB, iWarp and RoCE.
2) RDMA engine is disable by default. To enable it, execute the following
   before compile:

$ export EXTFLAGS="-DFIO_HAVE_RDMA"
$ export EXTLIBS="-libverbs -lrdmacm"

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>