Fix IPv6 Prefix ID default value

. Always initialize it to 0 when it's undefined
. Remove unecessary initializations and checks
. Bump config version to 9.5
. Write an upgrade config function to initialize old configs properly
Allow codel to be activated as an option for the specific queues or as its own discipline without any childs
Fixup gwlb functions related to gw failover

Make apinger pass the gateway parameter both when an alarm alarms (gateway is down) and when it comes good (gateway is up). This way the downstream openvpn and dyndns code can know what happened and do sensible stuff.
Return the friendly interface name ("wan", "opt1" etc) rather than the actual device name ("vr0", "vr1" etc). The openvpn and dynamic dns code that uses this needs to work with various entries in the config that all use the friendly interface name.
Handle gateway argument to rc.opnvpn

Various fixups to make this work. Now I can:
- Unplug an interface, any OpenVPN servers/clients in a gateway group using that interface are restarted and come up on the highest tier available interface. OpenVPN servers/clients that are only on that interface go down, of course.
- Plug in the cable again, any OpenVPN servers/clients in a gateway group using that interface are restarted and come up on the now-highest tier available interface (i.e. they fail back if the interface that just came up is higher tier). OpenVPN servers/clients that are only on that interface now come up.
Merge pull request #625 from phil-davis/master

Fixup handling gateway argument to rc.openvpn
Add includes to interfaces.inc

There were some includes needed when calling into here from rc.linkup - somehow everything else that calls interface_configure(p1, "true", p3) has already included these.
Reload routes etc when rc.linkup happens

When a link comes up, call interface_configure with p2=true. This makes it run various extra routines such as system_routing_configure - which will put back the default route or other static routes that might have been removed when the link was down.
Fixes for track6 interfaces:

. Do not remove link-local when it's already correct
. Let dhcp6c deal with tracked interface IP
Fix wrong check added on commit 1f64b66bf0 that was checking openvpn server twice and don't checking openvpn client
Merge pull request #626 from phil-davis/master

Restore default route after HOTPLUG linkup
Pull code from the calling place rather than the interfaces.inc
Optimize which OpenVPN instances are restarted
Remember which interface was used by each OpenVPN conf

When interfaces go down and up we need to know which interface (vr1, vr2 etc) each OpenVPN instance is using so we can optimize our decision about which instances to resync. That data is not in the conf file (the conf file contains the IP address the instance binds to). This change puts the interface name into a little file in /var/etc/openvpn for later use.
Revert "Fixes for track6 interfaces:"

It's not the correct fix

This reverts commit e8307ae03e2769bd0ebaa4b9441ac797b50a3800.
Merge pull request #627 from phil-davis/master

Optimize which OpenVPN instances are restarted