RDMA/core: Fix order of nldev_exit call

Create symmetrical exit flow by calling to nldev_exit() after
call to rdma_nl_unregister(RDMA_NL_LS).

Fixes: 6c80b41a ("RDMA/netlink: Add nldev initialization flows")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/64e676774a53a406f4cde265d5a4cfd6b8e97df9.1666683334.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>