xfs_bmap: fix -n documentation in manpage

xfs_bmap's manpage mis-describes the behavior of the
-n option.  xfs_io's fiemap command references the xfs_bmap
manpage, and has the same problem:

-n does not change the query batch size, it limits the number
of extents displayed.

This has been true for 15+ years, so change the documentation
to match reality.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/man/man8/xfs_bmap.8 b/man/man8/xfs_bmap.8
index 098cfae..c725519 100644
--- a/man/man8/xfs_bmap.8
+++ b/man/man8/xfs_bmap.8
@@ -77,12 +77,11 @@
 .BI \-n " num_extents"
 If this option is given,
 .B xfs_bmap
-obtains the extent list of the file in groups of
+will display at most
 .I num_extents
 extents. In the absence of
 .BR \-n ", " xfs_bmap
-queries the system for the number of extents in the file and uses that
-value to compute the group size.
+will display all extents in the file.
 .TP
 .B \-p
 If this option is used,