RDMA/{cma, ucma}: Simplify and rename rdma_set_ib_paths

Since 2006 there has been no user of rdmacm based application to make use
of setting multiple path records using rdma_set_ib_paths API.

Therefore code is simplified to allow setting one path record entry.
Now that it sets only single path, it is renamed to reflect the same.

Signed-off-by: Parav Pandit <parav@mellanox.com>
Reviewed-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>