treewide: use mirror tag @KERNEL where applicable

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

libs/dtc/Makefile

@@ -12,7 +12,7 @@ PKG_VERSION:=1.4.6
 PKG_RELEASE:=2
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 PKG_HASH:=382302bfcc3c40734be80ac620983971d911ec4cde798f551873f3eb008c7b7e
-PKG_SOURCE_URL:=https://www.kernel.org/pub/software/utils/dtc
+PKG_SOURCE_URL:=@KERNEL/software/utils/dtc
 PKG_LICENSE:=GPL-2.0
 PKG_LICENSE_FILES:=GPL
 PKG_INSTALL:=1

utils/kmod/Makefile

@@ -12,7 +12,7 @@ PKG_VERSION:=20
 PKG_RELEASE:=1
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
-PKG_SOURCE_URL:=https://www.kernel.org/pub/linux/utils/kernel/kmod/
+PKG_SOURCE_URL:=@KERNEL/linux/utils/kernel/kmod/
 PKG_HASH:=89c1a1a2193c31f9ebe582640bfa2bd401341dc24119f5a7f702588116fadaa0
 PKG_MAINTAINER:=Jeff Waugh <jdub@bethesignal.org>
 PKG_LICENSE:=LGPL-2.1+