mlxsw: spectrum_buffers: Allow skipping ingress port quota configuration

The CPU port is used to transmit traffic that is trapped to the host
CPU. It is therefore irrelevant to define ingress quota for it.

Add a 'skip_ingress' argument to the function tasked with configuring
per-port quotas, so that ingress quotas could be skipped in case the
passed local port is the CPU port.

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