net/icmpv6: Discard Neighbor Discovery packet if optlen is 0

This commit make ICMPv6 on NuttX compliant with RFC4861 ignoring
a Neighbor Discovery packet when its optlen is 0.

Signed-off-by: Alan C. Assis <acassis@gmail.com>

net/icmpv6/icmpv6_input.c

@@ -428,6 +428,15 @@ void icmpv6_input(FAR struct net_driver_s *dev, unsigned int iplen)
            FAR struct icmpv6_generic_s *opt =
                                 (FAR struct icmpv6_generic_s *)&options[ndx];
 
+            /* RFC 4861 4.6: "The value 0 is invalid. Nodes MUST silently
+             * discard a packet that contains an option with length zero."
+             */
+
+            if (opt->optlen == 0)
+              {
+                goto icmpv6_drop_packet;
+              }
+
             switch (opt->opttype)
               {
                 case ICMPv6_OPT_SRCLLADDR: