wifi: mt76: mt7996: Rely on msta_link link_id in mt7996_vif_link_remove()

wifi: mt76: mt7996: Rely on msta_link link_id in mt7996_vif_link_remove()

Rely on msta_link link_id value in mt7996_vif_link_remove routine
instead of using link_conf pointer. This assumption is correct since
msta_link link_id is set to link_conf link_id value in mt7996_vif_link_add
routine.
Moreover, fallback to default ieee80211_bss_conf struct if the link_conf
pointer in mt7996_vif_link_remove() is NULL.
MT7996 hw requires to remove AP MLD links from MCU configuration during
AP tear-down process (e.g. running mt7996_remove_interface()). Doing so,
we can't assume link_conf pointer is always non-NULL running
mt7996_vif_link_remove routine.

Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/20260315-mt7996-mlo-link-reconf-v1-1-a8a634fbc927@kernel.org
Signed-off-by: Felix Fietkau <nbd@nbd.name>