Config.in: put back legacy comment for BR2_ENABLE_SSP

Put back legacy comment for BR2_ENABLE_SSP which was dropped with commit
810ba387bec3c5b6904e8893fb4cb6f9d3717466

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

Config.in

@@ -728,7 +728,7 @@ comment "PIC/PIE needs a toolchain w/ PIE"
 
 choice
 	bool "Stack Smashing Protection"
-	default BR2_SSP_ALL if BR2_ENABLE_SSP
+	default BR2_SSP_ALL if BR2_ENABLE_SSP # legacy
 	default BR2_SSP_STRONG if BR2_TOOLCHAIN_HAS_SSP_STRONG
 	default BR2_SSP_REGULAR
 	depends on BR2_TOOLCHAIN_HAS_SSP