There doesn't appear to be a reason to do this, as only the last entry
is actually reserved for unknown multicast.
This also fixes two issues:
- As the increment happened after the bounds check, the value of the
actually reserved last entry could be overwritten.
- On deletion of entries, a corresponding decrement was missing,
causing the wrong entry to be marked as free.
Fixes: cde31976e3 ("realtek: Add support for Layer 2 Multicast")
Signed-off-by: Jan Hoffmann <jan@3e8.eu>
57df840670