borgbackup/borg#7181 (comment)

See there:

First all the changes from msgpack master were ported to our bundled msgpack in borgbackup 1.1-maint branch.

Then CI was failing. ntohs / ntohl undeclared.

Then the change that removed the include was reverted which made CI happy again.

So I guess you need to revert this change in master branch here also.

Note: the bundled msgpack in borg 1.1-maint is a slightly patched version 0.5.6, see there: https://github.com/borgbackup/borg/blob/e79986b2835291431f04683423304a02b039c0c1/src/borg/algorithms/msgpack/_version.py