config: kernel.org is now https-only

Every requests on kernel.org gets redirected to https.
So just set our kernel.org settings straight to begin with.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Config.in

@@ -186,7 +186,7 @@ config BR2_BACKUP_SITE
 
 config BR2_KERNEL_MIRROR
 	string "Kernel.org mirror"
-	default "http://www.kernel.org/pub"
+	default "https://www.kernel.org/pub"
 	help
 	  kernel.org is mirrored on a number of servers around the world.
 	  The following allows you to select your preferred mirror.