hostapd: Avoid sending client probe on removed client

hostapd: Avoid sending client probe on removed client

Sending client probe on already removed client from kernel driver does
not have any benefit and may lead unintended behavior among variable
drivers (mac80211 has a WARN_ON() that could have been triggered after
ifconfig down+up earlier when hostapd did not re-enable beaconing on
ifup). Skip this step in discussion when the kernel driver reports that
client entry is removed.

Signed-off-by: Peter Oh <poh@qca.qualcomm.com>