net: Disable NETIF_F_HW_TLS_RX when RXCSUM is disabled

With NETIF_F_HW_TLS_RX packets are decrypted in HW. This cannot be
logically done when RXCSUM offload is off.

Fixes: 14136564c8ee ("net: Add TLS RX offload feature")
Signed-off-by: Tariq Toukan <[e-mail]>
Reviewed-by: Boris Pismenny <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/networking/tls-offload.rst

···
 Disabling the latter implies clearing the former. Disabling TX checksum offload
 should not affect old connections, and drivers should make sure checksum
 calculation does not break for them.
+Similarly, device-offloaded TLS decryption implies doing RXCSUM. If the user
+does not want to enable RX csum offload, TLS RX device feature is disabled
+as well.

net/core/dev.c

···
 		}
 	}
 
+	if ((features & NETIF_F_HW_TLS_RX) && !(features & NETIF_F_RXCSUM)) {
+		netdev_dbg(dev, "Dropping TLS RX HW offload feature since no RXCSUM feature.\n");
+		features &= ~NETIF_F_HW_TLS_RX;
+	}
+
 	return features;
 }