[Linux] Device Outputs aren't being sent with output network set

[SeongGino]

Description

*Specifically referring to device outputs, not display output.
Trying to use the -output network option in MAME does not work - it seemingly isn't able to open the necessary port, thus no device output data is sent (e.g. for lightgun force feedback effects, LEDs, etc.)

Expected behavior

When the outputs option is enabled via [system]/mame/ini/mame.ini, I should be able to inspect the network traffic in localhost:8000 and see output data being sent.

Actual behavior

Port remains closed/inoperable, implying the option(s) does not even work. This DOES work in standalone MAME, implying it isn't an issue with the system (unless RA/libretro needs the user to be part of a specific group for this functionality?).

Steps to reproduce the bug

0. This issue specifically refers to Linux RetroArch, unless this also applies to Windows users
1. Install the latest MAME core.
2. Create a mame.ini in $system/mame/ini with the contents:

output network

3. Start a game in MAME (like term2).
4. In a terminal, type nc -v localhost 8000
5. Observe the error localhost [127.0.0.1] 8000 (irdmi): Connection refused

Version/Commit

• RetroArch: 1.16.0 (from Arch extra repository, and official AppImage release, with fresh configs)
• MAME (Current) Core: 0.261 (68520cf)

Environment information

• OS: Arch Linux

I've previously posted about this issue in the RetroArch frontend side here (libretro/RetroArch#15953), wondering if this is more an issue with the core, frontend, or my system in some manner and how to resolve.