debugfs: tidy up mmp handling

Several small fixes:

* Gracefully fail mmp commands if fs is not open
* Show magic number in dump_mmp command
* Fix header in output for set_mmp_value -l

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
2 files changed