kernel: generic: Add kernel 4.14 support

This adds initial support for kernel 4.14 based on the patches for
kernel 4.9.

In the configuration I deactivated some of the new possible security
features like:
CONFIG_REFCOUNT_FULL
CONFIG_SLAB_FREELIST_HARDENED
CONFIG_SOFTLOCKUP_DETECTOR
CONFIG_WARN_ALL_UNSEEDED_RANDOM

And these overlay FS options are also deactivated:
CONFIG_OVERLAY_FS_INDEX
CONFIG_OVERLAY_FS_REDIRECT_DIR

I activated this:
CONFIG_FORTIFY_SOURCE
CONFIG_POSIX_TIMERS
CONFIG_SLAB_MERGE_DEFAULT
CONFIG_WATCHDOG_HANDLE_BOOT_ENABLED

I am not sure if I did the porting correct for the following patches:
target/linux/generic/backport-4.14/020-backport_netfilter_rtcache.patch
target/linux/generic/hack-4.14/220-gc_sections.patch
target/linux/generic/hack-4.14/321-powerpc_crtsavres_prereq.patch
target/linux/generic/pending-4.14/305-mips_module_reloc.patch
target/linux/generic/pending-4.14/611-netfilter_match_bypass_default_table.patch
target/linux/generic/pending-4.14/680-NET-skip-GRO-for-foreign-MAC-addresses.patch

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/generic/hack-4.14/651-wireless_mesh_header.patch

@@ -0,0 +1,24 @@
+From 6d3bc769657b0ee7c7506dad9911111c4226a7ea Mon Sep 17 00:00:00 2001
+From: Imre Kaloz <kaloz@openwrt.org>
+Date: Fri, 7 Jul 2017 17:21:05 +0200
+Subject: mac80211: increase wireless mesh header size
+
+lede-commit 3d4466cfd8f75f717efdb1f96fdde3c70d865fc1
+Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
+---
+ include/linux/netdevice.h | 4 ++--
+ 1 file changed, 2 insertions(+), 2 deletions(-)
+
+--- a/include/linux/netdevice.h
++++ b/include/linux/netdevice.h
+@@ -138,8 +138,8 @@ static inline bool dev_xmit_complete(int
+ 
+ #if defined(CONFIG_HYPERV_NET)
+ # define LL_MAX_HEADER 128
+-#elif defined(CONFIG_WLAN) || IS_ENABLED(CONFIG_AX25)
+-# if defined(CONFIG_MAC80211_MESH)
++#elif defined(CONFIG_WLAN) || IS_ENABLED(CONFIG_AX25) || 1
++# if defined(CONFIG_MAC80211_MESH) || 1
+ #  define LL_MAX_HEADER 128
+ # else
+ #  define LL_MAX_HEADER 96