arg: fix incorrect default for backend sampling

[Galunid]

Overview

backend sampling was enabled, despite --help saying otherwise. It's been enabled since January, so I left the default as is and updated the docs. Let me know if you want backend sampling disabled, or experimental label removed

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: NO

[Galunid]

It is a mistake, I had multiple merged PRs in this repository (although none recently).

[ggerganov]

I don't think it is enabled by default:

llama.cpp/common/common.h

Lines 290 to 292 in c3a1128

	bool backend_sampling = false;

Most likely the issue is some disconnect between the backend parameters and the webui. Likely related to #18781. I think @allozaur is looking into this.

[Galunid]

That's possible, I retested with a different client and backend sampling was disabled, so it's related to webui.