When backporting the Don't Fragment UDP socket option, it was noticed
that the edns-udp-size probing uses 1432 as one of the values to be
probed and the documentation would be recommending 1400 as the safe
value. As the safe value can be from the 1400-1500 interval, the
documentation has been changed to match the probed value, so we do not
skip it.
Define a :gl: Sphinx role that takes a GitLab issue/MR number as an
argument and creates a hyperlink to the relevant ISC GitLab URL. This
makes it easy to reach ISC GitLab pages directly from the release notes.
Make all GitLab references in the release notes use the new Sphinx role.