default to latest 4.6.x for nios2

target/config/Config.in.kernelversion

@@ -5,6 +5,7 @@ choice
 prompt "Kernel version" if !ADK_TARGET_CHOOSE_ARCH
 depends on ADK_TARGET_OS_LINUX
 default ADK_TARGET_KERNEL_VERSION_4_6_1 if ADK_TARGET_ARCH_ARC
+default ADK_TARGET_KERNEL_VERSION_4_6_1 if ADK_TARGET_ARCH_NIOS2
 default ADK_TARGET_KERNEL_VERSION_4_6_1 if ADK_TARGET_ARCH_XTENSA && ADK_TARGET_WITHOUT_MMU
 default ADK_TARGET_KERNEL_VERSION_4_4_10