[FS#654] dial on demand not working

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - qxwd123 (qxwd123) 

Attached to Project - LEDE Project
Summary - dial on demand not working
Task Type - Bug Report
Category - Packages
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Medium
Priority - Very Low
Reported Version - lede-17.01
Due in Version - Undecided
Due Date - Undecided
Details - Using LEDE Reboot 17.01.0 r3205-59508e3 on Lenovo Y1.
After setting the Inactivity timeout to something not 0 in luci (option demand '5' in the config file),the dial procedure will be stopping at some stage,can't establish a connect.
And the log will be like this:
May  7 08:48:52 OpenWrt daemon.info pppd[9714]: Plugin rp-pppoe.so loaded.
May  7 08:48:52 OpenWrt daemon.info pppd[9714]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.5
May  7 08:48:52 OpenWrt daemon.notice pppd[9714]: pppd 2.4.5 started by root, uid 0
May  7 08:48:52 OpenWrt daemon.info pppd[9714]: Using interface pppoe-wan
May  7 08:48:52 OpenWrt daemon.notice pppd[9714]: local  IP address 10.64.64.64
May  7 08:48:52 OpenWrt daemon.notice pppd[9714]: remote IP address 10.112.112.112
Without the demand option everything works fine:
May  7 09:08:43 OpenWrt daemon.info pppd[2712]: Plugin rp-pppoe.so loaded.
May  7 09:08:43 OpenWrt daemon.info pppd[2712]: RP-PPPoE plugin version 3.8p compiled against pppd 2.4.5
May  7 09:08:43 OpenWrt daemon.notice pppd[2712]: pppd 2.4.5 started by root, uid 0
May  7 09:08:48 OpenWrt daemon.info pppd[2712]: PPP session is 9873
May  7 09:08:48 OpenWrt daemon.warn pppd[2712]: Connected to 00:30:88:1f:30:07 via interface eth2
May  7 09:08:48 OpenWrt daemon.info pppd[2712]: Using interface pppoe-wan
May  7 09:08:48 OpenWrt daemon.notice pppd[2712]: Connect: pppoe-wan  eth2
May  7 09:08:48 OpenWrt daemon.notice pppd[2712]: PAP authentication succeeded
May  7 09:08:48 OpenWrt daemon.notice pppd[2712]: peer from calling number 00:30:88:1F:30:07 authorized
May  7 09:08:49 OpenWrt daemon.notice pppd[2712]: local  IP address 93.232.124.118
May  7 09:08:49 OpenWrt daemon.notice pppd[2712]: remote IP address 217.0.119.51
May  7 09:08:49 OpenWrt daemon.notice pppd[2712]: primary   DNS address 217.0.43.17
May  7 09:08:49 OpenWrt daemon.notice pppd[2712]: secondary DNS address 217.0.43.49
(these logs is copy from the openwrt bug ticket[[https://dev.openwrt.org/ticket/13474|External Link]] because my log for this part had be override by massive "ieee80211 phy1: rt2x00queue_write_tx_frame: Error - Dropping frame due to full tx queue 2",sincere apology,smile)
It seems to be a historied legacy bug from Openwrt BB (or AA),and there is a solution by changing 2 files to make pppd disconnect when inactivity but can't re-dial:
1./etc/config/network, disable IPv6
config interface 'wan'
        option ipv6 0
2./lib/netifd/proto/ppp.sh: change nodefaultroute to defaultroute in the function of ppp_generic_setup()
	proto_run_command "$config" /usr/sbin/pppd \
		nodetach ipparam "$config" \
		ifname "$pppname" \
		${keepalive:+lcp-echo-interval $interval lcp-echo-failure ${keepalive%%[, ]*}} \
		${ipv6:++ipv6} \
		defaultroute \
Hope this stinking bug can be terminated in LEDE

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=654