Description of problem:

Cockpit trues to prefills the fstab mount options with appropriate values.  Currently this includes adding the "_netdev" option for iSCSI and NBD devices, and adding the workaround needed for filesystems on VDO volumes.

This prefilling works correctly when formatting a block device, but not when adding a filesystem to fstab later via the "Filesystem Mounting" dialog.  In that dialog, the options are prefilled, but they are computed as if they were for crypttab.

This makes a difference for VDO: the necessary workaround for filesystems on VDO volumes will not be prefilled.

Version-Release number of selected component (if applicable):
Cockpit 186 and earlier

How reproducible:
Always

Steps to Reproduce:
1. Create a VDO volume
2. Format it as xfs, say, with "Default" mounting
3. Open the "Filesystem Mounting" dialog and change to "Custom"

Actual results:
"Custom mount options" does not contains "x-systemd.requires=vdo.service"

Expected results:
"Custom mount options" does contains "x-systemd.requires=vdo.service"

Additional info:
Leaving out x-systemd.requires=vdo.service only makes a difference when the vdo.service unit is disabled.  When it is enabled, the _netdev option is enough to ensure proper ordering.  The vdo.service unit is enabled by default, so people will likely not run into any immediate trouble.