fix df m flag and missing suffix

[STRTSNM]

The df utility was missing the -m flag. And when running 'df -BM' it produces just raw numbers, without any suffix like GNU's df does.
Closes #11565

[oech3]

And cargo fmt.

[sylvestre]

and please add a test

[STRTSNM]

Updated! I've added tests, ran cargo fmt and added the Closes #tag .

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/misc/tty-eof (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/date/resolution (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cut/bounded-memory is now being skipped but was previously passing.
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.

[oech3]

CI still says cargo fmt is needed.

[STRTSNM]

All checks but one failed.

....
warning: spurious network error (1 try remaining): [6] Couldn't resolve host name (Could not resolve host: static.crates.io)
error: failed to download from `https://static.crates.io/crates/adler2/2.0.1/download`

Caused by:
[6] Couldn't resolve host name (Could not resolve host: static.crates.io)
make: *** [build-uudoc] Error 101
Make install failed! Exit code: 2 ...

So i've put an empty commit to rerun the jobs since it's just a network error

[STRTSNM]

Hey folks, just dropping a quick update.
I've resolved all the formatting discrepancies and all the checks have passed!!
Ready for review whenever you have a moment!