RDMA/cma: Pass QP type into rdma_create_id()

The RDMA CM currently infers the QP type from the port space selected
by the user.  In the future (eg with RDMA_PS_IB or XRC), there may not
be a 1-1 correspondence between port space and QP type.  For netlink
export of RDMA CM state, we want to export the QP type to userspace,
so it is cleaner to explicitly associate a QP type to an ID.

Modify rdma_create_id() to allow the user to specify the QP type, and
use it to make our selections of datagram versus connected mode.

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