rust: list: use consistent type parameter style

rust: list: use consistent type parameter style

Refer to the type parameters of `impl_has_list_links{,_self_ptr}!` by
the same name used in `impl_list_item!`. Capture type parameters of
`impl_list_item!` as `tt` using `{}` to match the style of all other
macros that work with generics.

Reviewed-by: Christian Schrefl <chrisi.schrefl@gmail.com>
Tested-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Link: https://lore.kernel.org/r/20250709-list-no-offset-v4-2-a429e75840a9@gmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>