xfs_repair: fix symlink target length checks by changing MAXPATHLEN to XFS_SYMLINK_MAXLEN

xfs_repair: fix symlink target length checks by changing MAXPATHLEN to XFS_SYMLINK_MAXLEN

XFS has a maximum symlink target length of 1024 bytes; this is a
holdover from the Irix days.  Unfortunately, the constant establishing
this was 'MAXPATHLEN', and is /not/ the same as the Linux MAXPATHLEN,
which is 4096.

The kernel enforces its 1024 byte MAXPATHLEN on symlink targets, but
xfsprogs picks up the (Linux) system 4096 byte MAXPATHLEN, which means
that xfs_repair doesn't complain about oversized symlinks.

Since this is an on-disk format constraint, put the define in the XFS
namespace.  As a side effect of the rename, xfs_repair wil detect
oversized symlinks and clean them off the system.

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