linux-headers: add support for 4.x versions

Signed-off-by: Jerzy Grzegorek <jerzy.grzegorek@trzebnica.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/linux-headers/linux-headers.mk

@@ -10,8 +10,10 @@
 LINUX_HEADERS_VERSION = $(call qstrip,$(BR2_DEFAULT_KERNEL_HEADERS))
 ifeq ($(findstring x2.6.,x$(LINUX_HEADERS_VERSION)),x2.6.)
 LINUX_HEADERS_SITE = $(BR2_KERNEL_MIRROR)/linux/kernel/v2.6
-else
+else ifeq ($(findstring x3.,x$(LINUX_HEADERS_VERSION)),x3.)
 LINUX_HEADERS_SITE = $(BR2_KERNEL_MIRROR)/linux/kernel/v3.x
+else ifeq ($(findstring x4.,x$(LINUX_HEADERS_VERSION)),x4.)
+LINUX_HEADERS_SITE = $(BR2_KERNEL_MIRROR)/linux/kernel/v4.x
 endif
 LINUX_HEADERS_SOURCE = linux-$(LINUX_HEADERS_VERSION).tar.xz