Some headers are not installed (Sanity Checks for 1.7.6 rc1)

Please verify the packages and files according to
https://wiki.isc.org/bin/view/QA/KeaReleaseProcess, "4. Sanity Checks" chapter
and your imagination.

!!!!!!!
Before starting any checks. please, state in Sanity Checks issue in GitLab
https://gitlab.isc.org/isc-projects/kea/issues/1161
what check you are doing in a thread/discussion (not as comment).
When you finish given check state in the same thread/discussion what is the result.
This way we know what is covered upfront and we can avoid repeating ourselves.
!!!!!!!

Release content is located on:
1) [tarballs] repo.isc.org in the following folders:
   /data/shared/sweng/kea/releases/1.7.6-rc1
   /data/shared/sweng/kea/releases/premium-1.7.6-rc1
   /data/shared/sweng/kea/releases/subscription-1.7.6-rc1

SHA256 (1.7.6-rc1/kea-1.7.6.tar.gz) = 1da3d50e0c8e92e1aa6d66100b5afd7b93ba2c50b0a4ea114fd9dcb8be982ca9
SHA256 (subscription-1.7.6-rc1/kea-subscription-1.7.6.tar.gz) = d32434fd112cbebce25f22d252cf3aca73483481ab166b09231e4db871b7733e
SHA256 (premium-1.7.6-rc1/kea-premium-1.7.6.tar.gz) = 47d7f3926a7d73511a21754a145be07c14b500f70aae58a7ec4550bc80cf47e1

2) [rpm/deb packages] on packages.isc.org, exact packages versions are stored here:
   https://jenkins.isc.org/job/kea-1.7/job/pkg/193/
   Release version is 1.7.6-isc0016720200323100957 (please verify if it is this version while installing).
   Install instruction is here: https://wiki.isc.org/bin/view/QA/KeaReleaseProcess, chapter 4. Sanity Checks, point 9.