wifi: mt76: mt7996: set link_valid field when initializing wcid

wifi: mt76: mt7996: set link_valid field when initializing wcid

[ Upstream commit 7eaea3a8ba1e9bb58f87e3030f6ce18537e57e1f ]

This ensures the upper layer uses the correct link ID during packet
processing.

Fixes: dd82a9e02c05 ("wifi: mt76: mt7996: Rely on mt7996_sta_link in sta_add/sta_remove callbacks")
Signed-off-by: Shayne Chen <shayne.chen@mediatek.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20251106064203.1000505-7-shayne.chen@mediatek.com
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Sasha Levin <sashal@kernel.org>