Release: Update BR defconfig to Linux 4.8

Follows the changes introduced in commit:

    62ab502 arc: Upgrade to Linux 4.8

Signed-off-by: Anton Kolesov <[email protected]>

Author: anthony-kolesov

extras/buildroot/axs103.defconfig

@@ -3,7 +3,7 @@ BR2_archs38=y
 BR2_TOOLCHAIN_EXTERNAL=y
 BR2_TOOLCHAIN_EXTERNAL_PATH="$(ARC_TOOLCHAIN_PATH)"
 BR2_TOOLCHAIN_EXTERNAL_GCC_6=y
-BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_7=y
+BR2_TOOLCHAIN_EXTERNAL_HEADERS_4_8=y
 BR2_TOOLCHAIN_EXTERNAL_LOCALE=y
 BR2_TOOLCHAIN_EXTERNAL_HAS_SSP=y
 BR2_TOOLCHAIN_EXTERNAL_INET_RPC=y