Munin 2.0.76 df plugin has issues with BusyBox df

[chapmajs]

Describe the bug
Munin's df plugin from v2.0.76 produces no output on Linux systems that use BusyBox's df (e.g. Alpine Linux) instead of GNU coreutils due to BusyBox's df not supporting some GNU switches (it fails with no output since Munin is redirecting stderr to /dev/null)

To Reproduce
Steps to reproduce the behavior:

1. Install munin-node on a Linux system that uses BusyBox and symlinks df to the BusyBox executable
2. As root, do munin-run df config
3. Observe a lack of output

Expected behavior
Munin df plugin expected to produce disk statistics for mounted filesystems.

Desktop (please complete the following information):

• OS+Distribution Version: Alpine Linux 3.20
• Munin Version: 2.0.76r0

Additional context
This problem does not appear on systems where GNU coreutils has been brought in by some other package, or installed explicitly. The Munin df plugin in v2.0.76 does not support the dfopts environment variable as newer versions do.

The offending switches are -l (show local filesystems only) and -x (excluded FS type list). Editing the source of the Munin df plugin and hardcoding it to only send the -P (POSIX output) switch causes the Munin df plugin to function properly with BusyBox df.

I can submit a PR to fix this, but I didn't know if that is even desirable or if this is an EWONTFIX.

[chapmajs]

Is this something that I should put together a PR for?