initramfs-scripts: require canmount=on for non-bootfs

[bar-g]

Motivation and Context

The current initramfs script even auto-mounts "canmount=noauto" filesystems.

If there really are any cases that depend on disobeying noauto besides the current bootfs= exception, it's generally preferable to instead allow limited automounting cleanly (as in 17996) for these cases.

This is a "drive-by" filing of a very small, and sensible change, proposed in
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1110397 and #17963

Description

Skip mounting if canmount != on instead of only canmount = off (i.e. also if canmount = noauto).

How Has This Been Tested?

not tested

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[bar-g]

Closing,

1. The original author of the script found the logic got corrupted with an intent to make the script portable: initramfs-scripts: more elegant canmount property handling? #17963 (comment)
2. The relaxation/disobeying of canmount=noauto is still an integral part needed for the active bootfs= boot environment, to auto-mount its sub-filesystems.
3. So, the case of the bug-report needs to be narrowed down, noauto can't be obeyed unconditionally. (At least until having a proper, selectively applicable, path-limiting canmount= allowance alternative for noauto: canmount bootfs:path -- simple & conflict-free multi-boot / shared zpool support #17996)