icmpv6: bail out for icmpv6.hdr keyword if not ICMPv6

(cherry picked from commit ddb4d289ae)

src/detect-icmpv6hdr.c

@@ -105,7 +105,10 @@ static InspectionBuffer *GetData(DetectEngineThreadCtx *det_ctx,
     InspectionBuffer *buffer = InspectionBufferGet(det_ctx, list_id);
     if (buffer->inspect == NULL) {
         uint32_t hlen = ICMPV6_HEADER_LEN;
-        DEBUG_VALIDATE_BUG_ON(p->icmpv6h == NULL);
+        if (p->icmpv6h == NULL) {
+            // DETECT_PROTO_IPV6 does not prefilter
+            return NULL;
+        }
         if (((uint8_t *)p->icmpv6h + (ptrdiff_t)hlen) >
                 ((uint8_t *)GET_PKT_DATA(p) + (ptrdiff_t)GET_PKT_LEN(p)))
         {