net: ipv6: Skip unknown options in NA message

If we receive unknown option in neighbor advertisement message,
then skip those properly. Old code did not check the length of
the extension options which could cause infinite loop.

Jira: ZEP-2219

Signed-off-by: Ruslan Mstoi <ruslan.mstoi@intel.com>

Author: Ruslan Mstoi

subsys/net/ip/ipv6.c

@@ -1662,7 +1662,7 @@ static enum net_verdict handle_na_input(struct net_pkt *pkt)
 					     net_pkt_ipv6_ext_opt_len(pkt) +
 					     (hdr->len << 3));
 
-		if (prev_opt_len == net_pkt_ipv6_ext_opt_len(pkt)) {
+		if (prev_opt_len >= net_pkt_ipv6_ext_opt_len(pkt)) {
 			NET_ERR("Corrupted NA message");
 			goto drop;
 		}