fix(lwip): Fix ping_v6 receiving to accept only echo replies

This fixes a bug where we ping our own IP and the request itself
bounces back to the raw receive function and is incorrectly treated as
reply. (this bug was discovered when fixing ICMPv6 pings with incorrect
checksums, while the ping request was dropped in icmpv6.c due to wrong
checksum, but was also fed to raw layers where it was treated as
"correct" response, so the PINGv6 to ourselves still worked)

Author: david-cermak

components/lwip/apps/ping/ping_sock.c

@@ -133,7 +133,8 @@ static int esp_ping_receive(esp_ping_t *ep)
             if (IP_IS_V6_VAL(recv_addr)) {      // Currently we process IPv6
                 struct ip6_hdr *iphdr = (struct ip6_hdr *)buf;
                 struct icmp6_echo_hdr *iecho6 = (struct icmp6_echo_hdr *)(buf + sizeof(struct ip6_hdr)); // IPv6 head length is 40
-                if ((iecho6->id == ep->packet_hdr->id) && (iecho6->seqno == ep->packet_hdr->seqno)) {
+                if ((iecho6->type == ICMP6_TYPE_EREP) // only check the ICMPv6 echo reply types
+                    && (iecho6->id == ep->packet_hdr->id) && (iecho6->seqno == ep->packet_hdr->seqno)) {
                     ip_addr_copy(ep->recv_addr, recv_addr);
                     ep->received++;
                     ep->recv_len = IP6H_PLEN(iphdr) - sizeof(struct icmp6_echo_hdr); //The data portion of ICMPv6