include: ring_buffer: fix storage class specifier in RING_BUF_* macros

[jfischer-no]

Despite documentation macros RING_BUF_*_DECLARE_* do not
define struct ring_buf as static. Add static specifier to
struct ring_buf in RING_BUF_*_DECLARE_* macros.

Fixes: #36608

[jfischer-no]

DNM since "The ring buffer can be accessed outside the module where it is defined using..." contradicts "Statically define and initialize a ... ring buffer."

[ycsin]

Fixed #36608

[carlescufi]

DNM since "The ring buffer can be accessed outside the module where it is defined using..." contradicts "Statically define and initialize a ... ring buffer."

@nordic-krch can you shed some light here?

[nordic-krch]

I think we need to remove word Statically and keep it global. I don't see an option to modify macro to allow something like static RING_BUF_DECLARE(foo). If static ring buffer macros are needed macro can be extended with option or new macro added.

[nordic-krch]

Created #37565

[jfischer-no]

close in favor of #37926