IB/core: Remove rdma_resolve_ip_route() as exported symbol

rdma_resolve_ip_route() is used only by ib_core module. Therefore it is
removed as an exported symbol.

Reviewed-by: Daniel Jurgens <danielj@mellanox.com>
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>