include: Do not alter KERNELRELEASE for external/git kernels

In case we use external and/or git cloned kernels, let the kernel
determine the appropriate KERNELRELEASE. We cannot used
LINUX_UNAME_VERSION because that one gets determined at a later time,
when the kernel is already built proper.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

include/kernel-defaults.mk

@@ -24,9 +24,14 @@ KERNEL_MAKEOPTS := -C $(LINUX_DIR) \
 	CONFIG_SHELL="$(BASH)" \
 	$(if $(findstring c,$(OPENWRT_VERBOSE)),V=1,V='') \
 	$(if $(PKG_BUILD_ID),LDFLAGS_MODULE=--build-id=0x$(PKG_BUILD_ID)) \
-	KERNELRELEASE=$(LINUX_VERSION) \
 	cmd_syscalls=
 
+
+ifeq ($(call qstrip,$(CONFIG_EXTERNAL_KERNEL_TREE))$(call qstrip,$(CONFIG_KERNEL_GIT_CLONE_URI)),)
+  KERNEL_MAKEOPTS += \
+	KERNELRELEASE=$(LINUX_VERSION)
+endif
+
 ifdef CONFIG_STRIP_KERNEL_EXPORTS
   KERNEL_MAKEOPTS += \
 	EXTRA_LDSFLAGS="-I$(KERNEL_BUILD_DIR) -include symtab.h"