scripts/download.pl: Use CDN for kernel downloads

Fixes #1059

patches/openwrt/0093-scripts-download.pl-Use-CDN-for-kernel-downloads.patch

+From: Petr Štetiar <ynezz@true.cz>
+Date: Mon, 23 May 2016 12:55:01 +0200
+Subject: scripts/download.pl: Use CDN for kernel downloads
+
+More info at https://www.kernel.org/introducing-fastly-cdn.html
+
+Signed-off-by: Petr Štetiar <ynezz@true.cz>
+
+Backport of LEDE e0b241bb489b82b42338a7469f5b5bd387f4c100
+
+diff --git a/scripts/download.pl b/scripts/download.pl
+index 111d03c63320d0c4f7b19902a4a5e23acb3b8a4d..ea4e2c4887b530236a9a56053105053e48a9c7b5 100755
+--- a/scripts/download.pl
++++ b/scripts/download.pl
+@@ -177,8 +177,8 @@ foreach my $mirror (@ARGV) {
+ 			push @extra, "$extra[0]/longterm/v$1";
+ 		}		
+ 		foreach my $dir (@extra) {
+-			push @mirrors, "ftp://ftp.all.kernel.org/pub/$dir";
+-			push @mirrors, "http://ftp.all.kernel.org/pub/$dir";
++			push @mirrors, "https://cdn.kernel.org/pub/$dir";
++			push @mirrors, "https://www.kernel.org/pub/$dir";
+ 		}
+     } elsif ($mirror =~ /^\@GNOME\/(.+)$/) {
+ 		push @mirrors, "http://ftp.gnome.org/pub/GNOME/sources/$1";