smb/client: Use EXPORT_SYMBOL_IF_KUNIT() to export symbols in SMB2

smb/client: Use EXPORT_SYMBOL_IF_KUNIT() to export symbols in SMB2

Replace EXPORT_SYMBOL_FOR_MODULES() with EXPORT_SYMBOL_IF_KUNIT()
to mark the symbols as visible only if CONFIG_KUNIT is enabled.

Kunit test should import the namespace EXPORTED_FOR_KUNIT_TESTING to
use these marked symbols. This is the standard way for all KUnit
tests.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>