configs: lock kernel version for atngw100_defconfig

The 3.10.x kernels fail to build with the following message:

vsprintf.c:(.text+0x17e0): relocation truncated to fit: R_AVR32_16N_PCREL against symbol `_ctype' defined in .text section in lib/lib.a(ctype.o)

While this is most likely a toolchain issue, but since AVR32 isn't a
well-maintained architecture, there's not much we can do.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

configs/atngw100_defconfig

@@ -1,6 +1,10 @@
 # Architecture
 BR2_avr32=y
 
+# Lock down kernel headers version, to match the kernel version used
+# below.
+BR2_KERNEL_HEADERS_3_9=y
+
 # Filesystems
 BR2_TARGET_ROOTFS_JFFS2=y
 BR2_TARGET_ROOTFS_JFFS2_FLASH_128=y
@@ -17,6 +21,10 @@ BR2_TARGET_UBOOT_BOARDNAME="atngw100"
 BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2010.09"
 
-# Kernel
+# Kernel. Locked to 3.9.x, because 3.10.x fails to build with
+# relocation truncated to fit: R_AVR32_16N_PCREL against symbol
+# `_ctype'
 BR2_LINUX_KERNEL=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION=y
+BR2_LINUX_KERNEL_CUSTOM_VERSION_VALUE="3.9.11"
 BR2_LINUX_KERNEL_DEFCONFIG="atngw100"