mac80211: HE STA disassoc due to QOS NULL not sent

In case of HE AP-STA link, ieee80211_send_nullfunc() will not
send the QOS NULL packet to check if AP is still associated.

In this case, probe_send_count will be non-zero and
ieee80211_sta_work() will later disassociate the AP, even
though no packet was ever sent.

Fix this by decrementing probe_send_count and not calling
ieee80211_send_nullfunc() in case of HE link, so that we
still wait for some time for the AP beacon to reappear and
don't disconnect right away.

Signed-off-by: Shay Bar <shay.bar@celeno.com>
Link: https://lore.kernel.org/r/20190703131848.22879-1-shay.bar@celeno.com
[clarify commit message]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>