wifi: mt76: mt7996: clear stale link state on full reset

In the Linux kernel, the following vulnerability has been resolved: wifi: mt76: mt7996: clear stale link state on full reset After a full chip reset, mac80211 reconfig replays interface, link and channel context setup. mt7996_vif_link_add() short-circuits when the link_id is still marked in mvif->valid_links, a state introduced for postponing link teardown to interface removal. The reset path frees the link structures without clearing those bits, so the replayed setup never re-creates dev_info/bss_info/STA records in the restarted firmware and never re-registers the link wcid, leaving the device inoperative. The reset path also leaks every allocated MLD index: per-link indices and the per-vif group/remap indices are re-allocated from scratch during reconfig, but the old bits stay set in the masks, so repeated full resets exhaust the index space. Clear valid_links in the reset vif iterator and reset the MLD index masks alongside the existing omac_mask clearing.