RDMA/cma: Expose private data when using AF_IB

If the source or destination address is AF_IB, then do not reserve a
portion of the private data in the IB CM REQ or SIDR REQ messages for
the cma header.  Instead, all private data should be exported to the
user.  When AF_IB is used, the rdma cm does not have sufficient
information to fill in the cma header.  Additionally, this will be
necessary to support any IB connection through the rdma cm interface,

Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>