RDMA/cma: Allow user to specify AF_IB when binding

Modify rdma_bind_addr to allow the user to specify AF_IB when binding
to a device.  AF_IB indicates that the user is not mapping an IP
address to the native IB addressing.  (The mapping may have already
been done, or is not needed)

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