mlxsw: spectrum_router: Correctly dump neighbour activity

mlxsw: spectrum_router: Correctly dump neighbour activity

The device's neighbour table is periodically dumped in order to update
the kernel about active neighbours. A single dump session may span
multiple queries, until the response carries less records than requested
or when a record (can contain up to four neighbour entries) is not full.
Current code stops the session when the number of returned records is
zero, which can result in infinite loop in case of high packet rate.

Fix this by stopping the session according to the above logic.

Fixes: 842a6e37f8ac ("mlxsw: spectrum_router: Periodically update the kernel's neigh table")
Signed-off-by: Arkadi Sharshevsky <arkadis@mellanox.com>
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>