bcm4908: enable & setup packet steering

Without packet steering NAT masquarade speed on BCM4908 /jumps/ between
two speeds:
1. 826 Mb/s (±3 Mb/s)
2. 909 Mb/s (±8 Mb/s)
and it never reaches ~940 Mb/s.

Proper packet steering can improve it. Below are testing results for
running iperf TCP traffic from LAN to WAN. They were used to pick up
golden values.

┌──────────┬──────────┬───────────┐
│   eth0   │  br-lan  │   speed   │
│ rps_cpus │ rps_cpus │   [Mbps]  │
├──────────┼──────────┼───────────┤
│        0 │        0 │ 743 / 804 │
│        0 │        1 │ 738 / 821 │
│        0 │        2 │     ✓ 940 │
│        0 │        4 │     ✓ 938 │
│        0 │        8 │     ✓ 941 │
├──────────┼──────────┼───────────┤
│        1 │        0 │       829 │
│        1 │        1 │       829 │
│        1 │        2 │     ✓ 942 │
│        1 │        4 │     ✓ 941 │
│        1 │        8 │     ✓ 941 │
├──────────┼──────────┼───────────┤
│        2 │        0 │     ✓ 942 │
│        2 │        1 │       926 │
│        2 │        2 │     ✓ 942 │
│        2 │        4 │     ✓ 942 │
│        2 │        8 │     ✓ 941 │
├──────────┼──────────┼───────────┤
│        4 │        0 │     ✓ 941 │
│        4 │        1 │       925 │
│        4 │        2 │     ✓ 941 │
│        4 │        4 │     ✓ 941 │
│        4 │        8 │     ✓ 941 │
├──────────┼──────────┼───────────┤
│        8 │        0 │     ✓ 942 │
│        8 │        1 │       925 │
│        8 │        2 │     ✓ 941 │
│        8 │        4 │     ✓ 942 │
│        8 │        8 │     ✓ 942 │
└──────────┴──────────┴───────────┘

Ref: fcbd39689e ("bcm53xx: enable & setup packet steering")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

target/linux/bcm4908/base-files/etc/init.d/fastnetwork

@@ -0,0 +1,46 @@
+#!/bin/sh /etc/rc.common
+
+START=25
+USE_PROCD=1
+
+start_service() {
+	reload_service
+}
+
+service_triggers() {
+	procd_add_reload_trigger "network"
+	procd_add_reload_trigger "firewall"
+	procd_add_reload_interface_trigger "lan"
+}
+
+reload_service() {
+	local packet_steering="$(uci -q get network.@globals[0].packet_steering)"
+	local num_cpus="$(grep -c "^processor.*:" /proc/cpuinfo)"
+	local flow_offloading="$(uci -q get firewall.@defaults[0].flow_offloading)"
+	local flow_offloading_hw="$(uci -q get firewall.@defaults[0].flow_offloading_hw)"
+	local rps_eth0=0
+	local rps_br_lan=0
+
+	[ "$num_cpus" -le 1 ] && return
+
+	[ "$packet_steering" = 1 ] && {
+		if [ ${flow_offloading_hw:-0} -gt 0 ]; then
+			# HW offloading
+			# Not implemented
+			:
+		elif [ ${flow_offloading:-0} -gt 0 ]; then
+			# SW offloading
+			# BCM4908 always reaches ~940 Mb/s
+			:
+		else
+			# Default
+			case "$num_cpus" in
+				2) rps_eth0=2; rps_br_lan=2;;
+				4) rps_eth0=e; rps_br_lan=e;;
+			esac
+		fi
+	}
+
+	echo $rps_eth0 > /sys/class/net/eth0/queues/rx-0/rps_cpus
+	echo $rps_br_lan > /sys/class/net/br-lan/queues/rx-0/rps_cpus
+}

target/linux/bcm4908/base-files/etc/uci-defaults/05_packet_steering

@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+uci set network.@globals[0].packet_steering="1"