Toggle to flush BSS entries when interface is disabled

Add globally configurable option to not flush cache when interface goes
down.

Bug: 73301881
Test: Verify that the connected MAC randomization ~3 second delay problem is gone
Test: b/122700105 regression testing completed

Change-Id: Ic1ec89afad3cd244858b95dcfdf5729b6522702a
diff --git a/wpa_supplicant/config_file.c b/wpa_supplicant/config_file.c
index 3a6dae5..1cdfbc2 100644
--- a/wpa_supplicant/config_file.c
+++ b/wpa_supplicant/config_file.c
@@ -1520,6 +1520,9 @@
 	if (config->p2p_interface_random_mac_addr)
 		fprintf(f, "p2p_interface_random_mac_addr=%d\n",
 			config->p2p_interface_random_mac_addr);
+	if (config->bss_no_flush_when_down)
+		fprintf(f, "bss_no_flush_when_down=%d\n",
+			config->bss_no_flush_when_down);
 
 }