lwip: Add patch to fix RA LLADDR processing (project-chip#29600)

* lwip: Add patch to fix RA LLADDR processing

* Fix weird spacing issue in patch.

* Restyled by prettier-markdown

* Add lladdr to wordlist

---------

Co-authored-by: Restyled.io <commits@restyled.io>

.github/.wordlist.txt

@@ -791,6 +791,8 @@ LightingApp
 LightingColor
 LightingState
 LinkSoftwareAndDocumentationPack
+lladdr
+LLADDR
 LocalConfigDisabled
 localedef
 localhost

src/lwip/patches/README.md

@@ -19,6 +19,14 @@ Troubleshooting: The patch uses the `ip6_addr_net_eq` function, which is a
 recent API change on upstream LwIP. The previous version of this function is
 `ip6_addr_netcmp`, so this function call may need to be replaced on older forks.
 
+### ND6 LLADDR fix
+
+This patch fixes a bug where the RA processing fails if the RA includes an
+LLADDR option with a hw address that is not the max length. This happens for
+thread devices.
+
+-   patch file: nd6_lladdr_fix.patch
+
 ## Important upstream patches
 
 ### Malformed neighbor solicitation packet fix

src/lwip/patches/nd6_lladdr_fix.patch

@@ -0,0 +1,24 @@
+diff --git a/src/core/ipv6/nd6.c b/src/core/ipv6/nd6.c
+index 55b5774f..8559d69b 100644
+--- a/src/core/ipv6/nd6.c
++++ b/src/core/ipv6/nd6.c
+@@ -686,14 +686,15 @@ nd6_input(struct pbuf *p, struct netif *inp)
+       switch (option_type) {
+       case ND6_OPTION_TYPE_SOURCE_LLADDR:
+       {
+-        struct lladdr_option *lladdr_opt;
+-        if (option_len < (ND6_LLADDR_OPTION_MIN_LENGTH + inp->hwaddr_len)) {
++        const u8_t option_type_and_length_size = 1 + 1;
++        const u8_t *addr_cursor;
++        if (option_len < (option_type_and_length_size + inp->hwaddr_len)) {
+           goto lenerr_drop_free_return;
+         }
+-        lladdr_opt = (struct lladdr_option *)buffer;
++        addr_cursor = buffer + option_type_and_length_size;
+         if ((default_router_list[i].neighbor_entry != NULL) &&
+             (default_router_list[i].neighbor_entry->state == ND6_INCOMPLETE)) {
+-          SMEMCPY(default_router_list[i].neighbor_entry->lladdr, lladdr_opt->addr, inp->hwaddr_len);
++          SMEMCPY(default_router_list[i].neighbor_entry->lladdr, addr_cursor, inp->hwaddr_len);
+           default_router_list[i].neighbor_entry->state = ND6_REACHABLE;
+           default_router_list[i].neighbor_entry->counter.reachable_time = reachable_time;
+         }