Remove rustls_result return value from rustls_server_config_builder_set_persistence

[jsha]

This function is currently:

rustls-ffi/src/server.rs

Lines 654 to 675 in 78736fb

	pub extern "C" fn rustls_server_config_builder_set_persistence(
	builder: *mut rustls_server_config_builder,
	get_cb: rustls_session_store_get_callback,
	put_cb: rustls_session_store_put_callback,
	) -> rustls_result {
	ffi_panic_boundary! {
	let get_cb: SessionStoreGetCallback = match get_cb {
	Some(cb) => cb,
	None => return rustls_result::NullParameter,
	};
	let put_cb: SessionStorePutCallback = match put_cb {
	Some(cb) => cb,
	None => return rustls_result::NullParameter,
	};
	let builder: &mut ServerConfigBuilder = try_mut_from_ptr!(builder);
	builder.session_storage = Some(Arc::new(SessionStoreBroker::new(
	get_cb, put_cb
	)));
	rustls_result::Ok
	}
	}
	}

Note that the only possible error return cases are that the inputs were NULL. Our API guidelines state that in such a case, we don't bother to return a rustls_result (and make the user check it), but instead do nothing and return void.

[cpu]

This looks easy to fix, but I'm not sure it's worth breaking semver for. In the primary rustls repo we have a next-major-release label for this. I've created the same here and applied it to this issue so we can think about knocking it out with the next big rustls update.