dchmod: fix check for CAP_CHOWN and CAP_FOWNER capabilities

[adammoody]

While adding the --open-noatime feature, it was discovered that mfu_flist_chmod was incorrectly checking for CAP_CHOWN and CAP_FOWNER capabilities. The old check would have reported that a process had such capabilities when it did not. This changes things to delegate the check to the new mfu_proc_set() function that was added for --open-noatime.

By default, mfu_flist_chmod should avoid trying to change the group or permissions of files that the current user does not own. However, due to wrong info about capabilities, it attempts the change and then reports an error:

>>:  dchmod --group g123 --mode g+X /path/to/file
[2023-10-11T11:59:19] Walking /path/to/file
[2023-10-11T11:59:19] Walked 1 items in 0.029 secs (34.693 items/sec) ...
[2023-10-11T11:59:19] Walked 1 items in 0.029 seconds (34.580 items/sec)
[2023-10-11T11:59:19] Changing 1 items
[2023-10-11T11:59:19] [0] [/path/to/src/common/mfu_flist_chmod.c:1021] ERROR: Failed to change ownership on `/path/to/file' lchown() (errno=1 Operation not permitted)
[2023-10-11T11:59:19] Processed 1 items in 0.013 seconds (75.637 items/sec) skipped/success/error chown=(0/0/1) chmod=(1/0/0)

With the fix, it now detects that it does not have permission to make the change, and so it correctly skips those files.

>>:  dchmod --group g123 --mode g+X /path/to/file
[2023-10-11T11:59:51] Walking /path/to/file
[2023-10-11T11:59:51] Walked 1 items in 0.009 secs (109.267 items/sec) ...
[2023-10-11T11:59:51] Walked 1 items in 0.009 seconds (108.450 items/sec)
[2023-10-11T11:59:51] Changing 1 items
[2023-10-11T11:59:51] Processed 1 items in 0.011 seconds (87.452 items/sec) skipped/success/error chown=(1/0/0) chmod=(1/0/0)

The end result is that dchmod prints fewer error messages when normal users change group or permission bits on a directory tree that contains files from a mix of different users. If needed, one can still force dchmod to attempt the change with --force.