net: ethernet: mtk_eth_soc: add missing ppe cache flush when deleting a flow

The cache needs to be flushed to ensure that the hardware stops offloading
the flow immediately.

Fixes: 33fc42de ("net: ethernet: mtk_eth_soc: support creating mac address based offload entries")
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20230330120840.52079-3-nbd@nbd.nameSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_ppe.c

@@ -459,6 +459,7 @@ __mtk_foe_entry_clear(struct mtk_ppe *ppe, struct mtk_flow_entry *entry)
 		hwe->ib1 &= ~MTK_FOE_IB1_STATE;
 		hwe->ib1 |= FIELD_PREP(MTK_FOE_IB1_STATE, MTK_FOE_STATE_INVALID);
 		dma_wmb();
+		mtk_ppe_cache_clear(ppe);
 	}
 	entry->hash = 0xffff;