[FS#1457] odhcpd annoucing dhcpv6 even when it's not enabled

[LEDE Bugs]

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

User who did this - Brian J. Murrell (brianjmurrell) 

Attached to Project - OpenWrt/LEDE Project
Summary - odhcpd annoucing dhcpv6 even when it's not enabled
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - High
Priority - Very Low
Reported Version - lede-17.01
Due in Version - Undecided
Due Date - Undecided
Details - Supply the following if possible:
 - Device problem occurs on
wndr4300
 - Software versions of OpenWrt/LEDE release, packages, etc.
17.01.4, r3560-79f57e422d
odhcpd - 2018-03-02-2da5850f-3
 - Steps to reproduce
/etc/config/dhcp snippet:

    config dhcp 'lan'
        option interface 'lan'
        option dhcpv6 'disabled'
        option ra 'server'
        option ra_management '1'
        list dns 'fd31:aeb1:48df::2'

Notice that "option dhcpv6 'disabled'" yet neighbour discovery is still saying DHCPv6 is available:

  $ sudo rdisc6 eth0
  Soliciting ff02::2 (ff02::2) on eth0...
  
  Hop limit                 :           64 (      0x40)
  Stateful address conf.    :          Yes
  ...

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=1457