smb/client: move smb2maperror declarations to smb2proto.h

smb/client: move smb2maperror declarations to smb2proto.h

For `smb2_error_map_table_test` and `smb2_error_map_num`, if their types
are changed in `smb2maperror.c` but the corresponding extern declarations
in `smb2maperror_test.c` are not updated, the compiler will not report an
error. Moving them to a common header file allows the compiler to catch
type mismatches.

Signed-off-by: ZhangGuoDong <zhangguodong@kylinos.cn>
Reviewed-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
Signed-off-by: Steve French <stfrench@microsoft.com>