net: wifi: shell: apply `struct option` as `static const`

This change marks the remaining instance of the `struct option` as
`static const`.

The rationale is that `struct option` is a read-only variable.
By using `static const`, we ensure immutability, leading to usage of only
the `.rodata` section and a reduction in the `.data` area.

Signed-off-by: Pisit Sawangvonganan <pisit@ndrsolution.com>