dnsmasq sometimes fails to start on 17.01.0

[Gui Iribarren]

Hello devs,
i'm trying to understand why dnsmasq is sometimes failing to start on
17.01.0
i added some "sleep"s and "logger" hooks to /etc/init.d/dnsmasq
http://pastebin.com/FV09f2jG

this is the result after a reboot
http://pastebin.com/1byQQ0a7

after ~4 seconds, the process dies without reason

if i manually do "/etc/init.d/dnsmasq restart" after boot, most of the
times everything goes well:
http://pastebin.com/CYVZmdiT
but *sometimes* even a manual "/etc/init.d/dnsmasq restart" will also
die without reason. After enough tries, it will start, of course.

i can reproduce the bug in some routers, and others apparently not (yet?).

I can reproduce it every boot on a tl-wdr3600 that is somewhere in the
local community network. I can use it to debug further at will.
I can't seem to reproduce it on a tl-wdr3500 that i have in my table
(but I could reproduce it yesterday many times with the same router,
which increases my confusion)

any pointer is much appreciated :)

ps: using lede
Reboot (17.01-SNAPSHOT, r3285-111cf1b)
built using SDK, so binaries are exactly the same as upstream
(thanks Daniel Golle for the suggestion, and Pau for doing the work!)