Fix RFID auto-link writing wrong cfs_rfid to non-RFID spools

When manually linking a slot, the code was writing the slot's rfid
field to Spoolman unconditionally. The K2 Plus CFS reports a non-empty
rfid value even for state=1 (manual, no chip) slots — likely a residual
value or bleed from an adjacent slot. This caused two different spools
to receive the same cfs_rfid, making auto-link map both slots to the
same Spoolman spool.

Fix: only write cfs_rfid to Spoolman when the CFS slot state is 2
(physical RFID chip confirmed present by the printer).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>