RDMA/core: Rename rdma_route.num_paths field to num_pri_alt_paths

RDMA/core: Rename rdma_route.num_paths field to num_pri_alt_paths

This fields means the total number of primary and alternative paths,
i.e.,:
  0 - No primary nor alternate path is available;
  1 - Only primary path is available;
  2 - Both primary and alternate path are available.
Rename it to avoid confusion as with follow patches primary path will
support multiple path records.

Signed-off-by: Mark Zhang <markzhang@nvidia.com>
Reviewed-by: Mark Bloch <mbloch@nvidia.com>
Link: https://lore.kernel.org/r/cbe424de63a56207870d70c5edce7c68e45f429e.1662631201.git.leonro@nvidia.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>