The master branch is the original lwip 2.0.2. The ndext branch is the one that extend the nd6.
Totoally, 4 files involed:
(1)icmp6.c, accpet rs;
(2)netif.h, add ra related variables;
(3)netic.c, add initilization of ra variables in netif_add and in netif_issue_reports (including one netif_create_ip6_linklocal_address fix);
(4)nd6.c, add rs handling in nd6_input, add ra sending in nd6_tmr, add nd6_send_ra, fix nd6_cleanup_netif issue.
@todo rs handling just skip the handling of the link layer address option which should be done.