[nrf noup] zephyr: Fix clearing the beacon set flag

fixup! [nrf noup] zephyr: Implement basic AP ops

Without this the management frame registrations are skipped causing
issue with scanning and association.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

src/drivers/driver_zephyr.c

@@ -1580,6 +1580,7 @@ int wpa_drv_zep_stop_ap(void *priv)
 	}
 
 	if_ctx->freq = 0;
+	if_ctx->beacon_set = false;
 out:
 	return ret;
 }