mlxsw: spectrum_qdisc: Distinguish between ingress and egress triggers

The following patches will configure the MLXSW_SP_SPAN_TRIGGER_ECN
mirroring trigger. This trigger is considered "egress", unlike the
previously-offloaded _EARLY_DROP. Add a helper to spectrum_span,
mlxsw_sp_span_trigger_is_ingress(), to classify triggers to ingress and
egress. Pass result of this instead of hardcoding true when calling
mlxsw_sp_span_analyzed_port_get()/_put().

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>