if_ovpn tests: skip float and linklocal test on < 2.7

[kp]

Summary

Earlier versions (than 2.7.0) do not support float notifications or link-local
addresses. Skip the relevant tests there.

PR: 289150
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")

[guest-svmhdvn]

Instead of skipping these and keeping around lots of code to check the ovpn version, why not just temporarily xfail them like I've done in the attached patch of https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=289150? That way, once Ports contains ovpn>=2.7, these tests will automatically start failing again with the message "failed: expected failure, but none found". We can remove the xfails promptly afterwards.

[kp]

In D52234#1193199, @guest-svmhdvn wrote:

Instead of skipping these and keeping around lots of code to check the ovpn version, why not just temporarily xfail them like I've done in the attached patch of https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=289150? That way, once Ports contains ovpn>=2.7, these tests will automatically start failing again with the message "failed: expected failure, but none found". We can remove the xfails promptly afterwards.

Because temporary changes have a way of becoming permanent, and this way we only have to change things once rather than twice. And it's entirely possible that we'll have similar issues in the future.