[][Add necessary patch and config for NF_HNAT]

[Description]
Add necessary patch and config for NF_HNAT.
	- patch : for resolving IPv6 expand headroom issue
	- config : for enabling NETFILTER by default

[Release-log]
N/A

Change-Id: Iffce551fd9caeb3e36911c2d45e5127a98682d1c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/4712981
diff --git a/target/linux/mediatek/patches-5.4/1001-mtkhnat-ipv6-fix-pskb-expand-head-limitation.patch b/target/linux/mediatek/patches-5.4/1001-mtkhnat-ipv6-fix-pskb-expand-head-limitation.patch
new file mode 100644
index 0000000..72719c8
--- /dev/null
+++ b/target/linux/mediatek/patches-5.4/1001-mtkhnat-ipv6-fix-pskb-expand-head-limitation.patch
@@ -0,0 +1,22 @@
+diff --git a/net/core/skbuff.c b/net/core/skbuff.c
+index 5ba1c72f..f4239459 100644
+--- a/net/core/skbuff.c
++++ b/net/core/skbuff.c
+@@ -69,6 +69,7 @@
+ #include <net/ip6_checksum.h>
+ #include <net/xfrm.h>
+ #include <net/mpls.h>
++#include <net/ra_nat.h>
+ 
+ #include <linux/uaccess.h>
+ #include <trace/events/skb.h>
+@@ -1666,6 +1667,9 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
+ 	       skb_shinfo(skb),
+ 	       offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
+ 
++	/*headroom copy*/
++	memcpy(data, skb->head, FOE_INFO_LEN);
++
+ 	/*
+ 	 * if shinfo is shared we must drop the old head gracefully, but if it
+ 	 * is not we can just drop the old head and let the existing refcount