wifi: iwlwifi: mvm: fix a crash when we run out of stations

In the Linux kernel, the following vulnerability has been resolved:

wifi: iwlwifi: mvm: fix a crash when we run out of stations

A DoS tool that injects loads of authentication frames made our AP

crash. The iwl_mvm_is_dup() function couldn't find the per-queue

dup_data which was not allocated.

The root cause for that is that we ran out of stations in the firmware

and we didn't really add the station to the firmware, yet we didn't

return an error to mac80211.

Mac80211 was thinking that we have the station and because of that,

sta_info::uploaded was set to 1. This allowed

ieee80211_find_sta_by_ifaddr() to return a valid station object, but

that ieee80211_sta didn't have any iwl_mvm_sta object initialized and

that caused the crash mentioned earlier when we got Rx on that station.