Ticket #3484 Note that for now prefixlen is useless in ipv6 tunnels. IPv4 accepts them
Merge pull request #983 from N0YB/RELENG_2_1

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Fixes #3484. Provide a dynamic gateway for gif v6 tunnels so it can be used on firewall rules etc. The guide for setting up this tunnels on docs need to change to leave the gif interface as none type. People upgrading need to fix this themselves with a not on release notes. This can be fixed if the kernel condition is relaxed to allow setting the prefixlen on the tunnel as ipv4
Ticket #3484 Correct the case for GRE tunnels as well since they behave the same. GRE seems to need the prefixlen 128 specified all the time so do it explicitly to be on safe side
Add a file flag to trigger the forced serial or else we may miss it during a firmware update and still end up with an accidentally disabled port.
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Firewall - NAT - Npt - Edit