ext4: rationalize ext4_extents.h inclusion

Previously, ext4_extents.h was being included at the end of ext4.h,
which was bad for a number of reasons: (a) it was not being included
in the expected place, and (b) it caused the header to be included
multiple times.  There were #ifdef's to prevent this from causing any
problems, but it still was unnecessary.

By moving the function declarations that were in ext4_extents.h to
ext4.h, which is standard practice for where the function declarations
for the rest of ext4.h can be found, we can remove ext4_extents.h from
being included in ext4.h at all, and then we can only include
ext4_extents.h where it is needed in ext4's source files.

It should be possible to move a few more things into ext4.h, and
further reduce the number of source files that need to #include
ext4_extents.h, but that's a cleanup for another day.

Reported-by: Sachin Kamat <sachin.kamat@linaro.org>
Reported-by: Wei Yongjun <weiyj.lk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 66a4e20..856206f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -45,12 +45,11 @@
 #include <linux/freezer.h>
 
 #include "ext4.h"
-#include "ext4_extents.h"
+#include "ext4_extents.h"	/* Needed for trace points definition */
 #include "ext4_jbd2.h"
 #include "xattr.h"
 #include "acl.h"
 #include "mballoc.h"
-#include "ext4_extents.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/ext4.h>