shadowsocks-libev: ignore error from flushing route table

Linux kernel and iproute2 together now implement strict checking of the
existence of route tables.

Previously kernel does not support filtering by table id, now it does
and will error with nlmsgerr "ipv4: FIB table does not exist".

Previously iproute2 dump all routes and filter by table id in userspace,
now this has changed with iproute2 commit c7e6371bc4af ("ip route: Add
protocol, table id and device to dump request")

Error scene

	root@OpenWrt:/# ip route flush table 100
	Error: ipv4: FIB table does not exist.
	Flush terminated
	root@OpenWrt:/# echo $?
	2

Fixes: openwrt#12095
Ref: https://lists.openwall.net/netdev/2019/05/02/105
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

net/shadowsocks-libev/Makefile

@@ -1,5 +1,5 @@
 #
-# Copyright (C) 2017-2019 Yousong Zhou <yszhou4tech@gmail.com>
+# Copyright (C) 2017-2020 Yousong Zhou <yszhou4tech@gmail.com>
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -14,7 +14,7 @@ include $(TOPDIR)/rules.mk
 #
 PKG_NAME:=shadowsocks-libev
 PKG_VERSION:=3.3.4
-PKG_RELEASE:=1
+PKG_RELEASE:=2
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.gz
 PKG_SOURCE_URL:=https://github.com/shadowsocks/shadowsocks-libev/releases/download/v$(PKG_VERSION)

net/shadowsocks-libev/files/ss-rules

@@ -154,7 +154,7 @@ ss_rules_flush() {
 
 	iptables-save --counters | grep -v ss_rules_ | iptables-restore --counters
 	while ip rule del fwmark 1 lookup 100 2>/dev/null; do true; done
-	ip route flush table 100
+	ip route flush table 100 2>/dev/null || true
 	for setname in $(ipset -n list | grep "ss_rules${o_af}_"); do
 		ipset destroy "$setname" 2>/dev/null || true
 	done