mlxsw: spectrum_router: Properly name netevent work struct

The struct containing the work item queued from the netevent handler is
named after the only event it is currently used for, which is neighbour
updates.

Use a more appropriate name for the struct, as we are going to use it
for more events.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>