bcm53xx: disable GRO by default at kernel level

This improves NAT masquarade network performance.

An alternative to kernel change would be runtime setup but that requires
ethtool and identifying relevant network interface and all related
switch ports interfaces.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

target/linux/bcm53xx/patches-5.10/600-net-disable-GRO-by-default.patch

@@ -0,0 +1,36 @@
+From: =?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?= <rafal@milecki.pl>
+Date: Mon, 20 Jun 2022 10:01:18 +0200
+Subject: [PATCH] net: disable GRO by default
+MIME-Version: 1.0
+Content-Type: text/plain; charset=UTF-8
+Content-Transfer-Encoding: 8bit
+
+In many cases GRO improves network performance however it comes at a
+cost of chacksums calculations. In case of slow CPU and missing hardware
+csum calculation support GRO can actually decrease network speed.
+
+On BCM4708 *disabling* GRO results in following NAT masquarade speed
+changes:
+1. 364 Mb/s → 396 Mb/s (packet steering disabled)
+2. 341 Mb/s → 566 Mb/s (packet steering enabled)
+
+Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
+---
+ include/linux/netdev_features.h | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/include/linux/netdev_features.h
++++ b/include/linux/netdev_features.h
+@@ -231,10 +231,10 @@ static inline int find_next_netdev_feature(u64 feature, unsigned long start)
+ #define NETIF_F_UPPER_DISABLES	NETIF_F_LRO
+
+ /* changeable features with no special hardware requirements */
+-#define NETIF_F_SOFT_FEATURES	(NETIF_F_GSO | NETIF_F_GRO)
++#define NETIF_F_SOFT_FEATURES	(NETIF_F_GSO)
+
+ /* Changeable features with no special hardware requirements that defaults to off. */
+-#define NETIF_F_SOFT_FEATURES_OFF	NETIF_F_GRO_FRAGLIST
++#define NETIF_F_SOFT_FEATURES_OFF	(NETIF_F_GRO_FRAGLIST | NETIF_F_GRO)
+
+ #define NETIF_F_VLAN_FEATURES	(NETIF_F_HW_VLAN_CTAG_FILTER | \
+ 				 NETIF_F_HW_VLAN_CTAG_RX | \