When trapping packets for on-CPU processing, Spectrum machines
differentiate between control and non-control traps. Traffic trapped
through non-control traps is treated as data and kept in shared buffer in
pools 0-4. Traffic trapped through control traps is kept in the dedicated
control buffer 9. The advantage of marking traps as control is that
pressure in the data plane does not prevent the control traffic to be
processed.

When the LLDP trap was introduced, it was marked as a control trap. But
then in commit aed4b572 ("mlxsw: spectrum: PTP: Hook into packet
receive path"), PTP traps were introduced. Because Ethernet-encapsulated
PTP packets look to the Spectrum-1 ASIC as LLDP traffic and are trapped
under the LLDP trap, this trap was reconfigured as non-control, in sync
with the PTP traps.

There is however no requirement that PTP traffic be handled as data.
Besides, the usual encapsulation for PTP traffic is UDP, not bare Ethernet,
and that is in deployments that even need PTP, which is far less common
than LLDP. This is reflected by the default policer, which was not bumped
up to the 19Kpps / 24Kpps that is the expected load of a PTP-enabled
Spectrum-1 switch.

Marking of LLDP trap as non-control was therefore probably misguided. In
this patch, change it back to control.
Reported-by: Maksym Yaremchuk <maksymy@nvidia.com>
Signed-off-by: Petr Machata <petrm@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>