Without this change calling `Xorg -displayfd ..` would always make X to use
:0 as the DISPLAY. This was a showstopper for running parallel desktop sessions.
The leftover UDS' are cleaned up during system's boot by the /etc/rc.d/cleartmp
service.
Based on work of jbeich and Olivier Certner <olivier.freebsd@free.fr>.
PR: 253277
Approved by: manu
Sponsored by: Serenity Cybersecurity, LLC
Differential Revision: https://reviews.freebsd.org/D30557
3312d02769