xfs: consolidate extent swap code

So we don't need xfs_dfrag.h in userspace anymore, move the extent
swap ioctl structure definition to xfs_fs.h where most of the other
ioctl structure definitions are.

Now that we don't need separate files for extent swapping, separate
the basic file descriptor checking code to xfs_ioctl.c, and the code
that does the extent swap operation to xfs_bmap_util.c.  This
cleanly separates the user interface code from the physical
mechanism used to do the extent swap.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
index 55a3072..d3ab953 100644
--- a/fs/xfs/xfs_ioctl32.c
+++ b/fs/xfs/xfs_ioctl32.c
@@ -33,7 +33,6 @@
 #include "xfs_inode.h"
 #include "xfs_itable.h"
 #include "xfs_error.h"
-#include "xfs_dfrag.h"
 #include "xfs_fsops.h"
 #include "xfs_alloc.h"
 #include "xfs_rtalloc.h"
@@ -643,7 +642,7 @@
 		error = mnt_want_write_file(filp);
 		if (error)
 			return error;
-		error = xfs_swapext(&sxp);
+		error = xfs_ioc_swapext(&sxp);
 		mnt_drop_write_file(filp);
 		return -error;
 	}