dhcp6c lock files not removed after unclean shutdown when using "Do not wait for an RA" on IPv6 WAN interface
When using a WAN connection with IPv6 that requires the "Do not wait for an RA" option if the router has an unclean shutdown and reboot (power outage) the dhcp6c_$interface_lock file(s) will still be in /tmp, meaning that dhcp6c will not start leaving the IPv6 interface(s) in limbo. (In this state I've had the WAN interface get a local-link address and the IPv6 gateway would be "pending", or sometimes with 100% packet loss).
I've attached a patch to rc.bootup that before the interfaces are set up it iterates over interfaces in $config that use DHCP6, and if a lock file is present in /tmp it removes the file. This solves the issue in my extensive testing last night.
I've gotten Martin to review the patch and implemented some suggestions of his.
This patch applies cleanly to 2.4.0-RELEASE, 2.4.2-RC, and 2.4.3.a.20171117.1226 in my testing.