posix: CONFIG_POSIX_API and CONFIG_NET_SOCKETS_POSIX_NAMES don't make sense to use together, and conflict when doing so

[pfalcon]

As discussed in #16009 .

The meaning of CONFIG_SOCKETS_POSIX_NAMES is "expose Zephyr's namespaced socket API under standard POSIX names".

The meaning of CONFIG_POSIX_API is "expose all POSIX APIs which are available in Zephyr".

From this description, it's clear that these 2 options shouldn't be used together, as CONFIG_POSIX_API has wider scope which subsumes and supersedes meaning of CONFIG_SOCKETS_POSIX_NAMES.

However, implementation-wise, these 2 options are implemented differently, so if someone by mistake enabled them, that can lead to compile-time errors (whose reason may be not immediately clear.

Consequently, we should:

• Either make these 2 options conflict, with explicit error message describing the above, or
• Make CONFIG_POSIX_API silently subsume CONFIG_SOCKETS_POSIX_NAMES.

[carlescufi]

Relabeling as enhancement since this is about the meaning of Kconfig options.

[pfalcon]

Relabeling as enhancement since this is about the meaning of Kconfig options.

Interesting, then why @nashif blocks a legitimate pull request #16009 , based on this unrelated enhancement?