udev-node: skip stack directory creation for diskseq

udev-node: skip stack directory creation for diskseq

The disk/by-diskseq symlink should not be shared with multiple block
devices. Hence, it is not necessary to create stack directory for the
symlink that manages which device owns the symlink.

This is not just a optimization.
If a service unit tries to mount a disk image but the service fails, then
the diskseq of the loop device for the image may be continuously increased
during restart, and inodes in /run may increase rapidly, as the stack
directories are cleaned up only when udev queue is empty.

Fixes #34637.