ports.7: Update dialog4ports to portconfig

dialog4ports has been replaced with portconfig for several years.
It was marked as deprecated and broken in ports:61e4a788ecab.
While here, tag SPDX.

MFC after: 3 days
Reported by: Community Discord
Reviewed by: bapt (previous version), mhorne
Approved by: mhorne (mentor)
Differential Revision: https://reviews.freebsd.org/D49204

(cherry picked from commit 3bf433f141a5c8987f347c6618bab0482063a66c)