net: dsa: rtl8366rb: don't prompt users for LED control

Make NET_DSA_REALTEK_RTL8366RB_LEDS a hidden symbol.
It seems very unlikely user would want to intentionally
disable it.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250228004534.3428681-1-kuba@kernel.org


Signed-off-by: Paolo Abeni <pabeni@redhat.com>