Create and use our own copy of linux/ext2_fs.h

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

e2fsprogs/tune2fs.c

@@ -8,13 +8,7 @@
  */
 #include "libbb.h"
 #include <linux/fs.h>
-/*
- * Work around linux/ext2_fs.h breakage.
- * See https://bugzilla.kernel.org/show_bug.cgi?id=42986.
- */
-typedef mode_t bb__umode_t;
-#define umode_t bb__umode_t
-#include <linux/ext2_fs.h>
+#include "bb_linux_ext2_fs.h"
 
 // storage helpers
 char BUG_wrong_field_size(void);