FreeBSD: Lock vnode in zfs_ioctl()

[amotin]

Previously vnode was not locked there, unlike Linux. It required locking it in vn_flush_cached_data(), which recursed on the lock if called from zfs_clone_range(), having the vnode locked.

Closes #16789

How Has This Been Tested?

Minimally. Run cp without block cloning and fsx from #16789.

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)
• 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.