OpenSSH 8.7p1 update for the base system

I'm preparing to update OpenSSH in the FreeBSD base system to 8.7p1,
and am sharing an initial patch for testing.

The update is available from a branch in my github repo:
https://github.com/emaste/freebsd/tree/openssh-8.7p1-wip
(commit 0afe07936bbd37a1b91ead95f580c47ccc16df79)

Also as a diff against main:
https://people.freebsd.org/~emaste/openssh/FreeBSD-base-openssh-8.7p1-20210904-114623.diff

In addition I have a review open in Phabricator, although it is quite
awkward to usefully review a vendor update presented like this.
https://reviews.freebsd.org/D29985

If you give it a try please let me know what you've tested out.