AP: Reset STA timeout_next on driver-based-SME association

AP: Reset STA timeout_next on driver-based-SME association

The next ap_handle_timer action was already cleared when association
is handled with user space -based SME. However, this step was missing
from the driver callback for indicating new association. This could
result in the first ap_handle_timer timeout on the new association
removing the station unexpectedly. Fix this by resetting the timeout_next
in hostapd_notif_assoc().

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>
intended-for: hostap-1