kernel: r8168: add missing flags

PKG_MAKE_FLAGS is required when compiling r8168-rss

Signed-off-by: Andy Chiang <AndyChiang_git@outlook.com>
Link: https://github.com/openwrt/openwrt/pull/20001
Signed-off-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
(cherry picked from commit 5719d6506467285db424814433e7b6d8779ee9d2)

package/kernel/r8168/Makefile

@@ -2,7 +2,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=r8168
 PKG_VERSION:=8.055.00
-PKG_RELEASE:=3
+PKG_RELEASE:=4
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.bz2
 PKG_SOURCE_URL:=https://github.com/openwrt/rtl8168/releases/download/$(PKG_VERSION)
@@ -40,6 +40,7 @@ endif
 
 define Build/Compile
 	+$(KERNEL_MAKE) $(PKG_JOBS) \
+		$(PKG_MAKE_FLAGS) \
 		M="$(PKG_BUILD_DIR)/src" \
 		modules
 endef