From `ip-link(8)`:
> [no]ignore-df - enables/disables IPv4 DF
suppression on this tunnel. Normally datagrams
that exceed the MTU will be fragmented; the
presence of the DF flag inhibits this, resulting
instead in an ICMP Unreachable (Fragmentation
Required) message. Enabling this attribute causes
the DF flag to be ignored.
If this option is enabled for a GRE/GRETAP tunnel, the `DF` flag in the outer IP header
will not inherit the inner IP header's `DF` flag.
This is useful to transfer packets that exceed the MTU of the underlay
network.
Those are all consumed by our parser, so they all support comments.
I was considering whether they should have a license header at all,
but in the end I decided to add it because those files are often created
by copying parts of real unit files. And if the real ones have a license,
then those might as well. It's easier to add it than to make an exception.
