atl1c: enable rx csum offload on Mikrotik 10/25G NIC

Mikrotik 10/25G NIC supports hw checksum verification on rx for
IP/IPv6 + TCP/UDP packets. HW checksum offload helps reduce host
cpu load.

This enables the csum offload specifically for Mikrotik 10/25G NIC
as other HW supported by the driver is known to have problems with it.

TCP iperf3 to Threadripper 3960X with NIC improved 16.5 -> 20.0 Gbps
with mtu=1500.
Signed-off-by: Gatis Peisenieks <gatis@mikrotik.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/atheros/atl1c/atl1c.h

@@ -241,6 +241,8 @@ struct atl1c_tpd_ext_desc {
 #define RRS_PACKET_PROT_IS_IPV6_ONLY(word) \
 	((((word) >> RRS_PROT_ID_SHIFT) & RRS_PROT_ID_MASK) == 6)
 
+#define RRS_MT_PROT_ID_TCPUDP	BIT(19)
+
 struct atl1c_recv_ret_status {
 	__le32  word0;
 	__le32	rss_hash;

drivers/net/ethernet/atheros/atl1c/atl1c_main.c

@@ -1671,6 +1671,11 @@ static irqreturn_t atl1c_intr(int irq, void *data)
 static inline void atl1c_rx_checksum(struct atl1c_adapter *adapter,
 		  struct sk_buff *skb, struct atl1c_recv_ret_status *prrs)
 {
+	if (adapter->hw.nic_type == athr_mt) {
+		if (prrs->word3 & RRS_MT_PROT_ID_TCPUDP)
+			skb->ip_summed = CHECKSUM_UNNECESSARY;
+		return;
+	}
 	/*
 	 * The pid field in RRS in not correct sometimes, so we
 	 * cannot figure out if the packet is fragmented or not,