Revert "pam_systemd: drop setting DBUS_SESSION_BUS_ADDRESS"

Revert "pam_systemd: drop setting DBUS_SESSION_BUS_ADDRESS"

This reverts commit 2b2b7228bffef626fe8e9f131095995f3d50ee3b.

Fixes #11293.

Removing the environment variable causes problems, e.g. Xfce and Chromium and
... don't communicate with the running dbus instance. If they attempt to start their
own instance, things become even more confusing. Those packages could be fixed
one by one, but removing the variable right now is causing too many problems.

(cherry picked from commit 00efd4988b8e4a147f96337de32e54925640f0b7)
(cherry picked from commit 6c44e6c681e55f8291078b51c72cbfd81cc21a94)

Gbp-Pq: Name Revert-pam_systemd-drop-setting-DBUS_SESSION_BUS_ADDRESS.patch