net/eth: Check iovec has enough data earlier

We want to check fields from ip6_ext_hdr_routing structure
and if correct read the full in6_address. Let's directly check
if our iovec contains enough data for everything, else return
early.

Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Miroslav Rezanina <mrezanin@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/eth.c

@@ -409,7 +409,7 @@ _eth_get_rss_ex_dst_addr(const struct iovec *pkt, int pkt_frags,
     size_t input_size = iov_size(pkt, pkt_frags);
     size_t bytes_read;
 
-    if (input_size < ext_hdr_offset + sizeof(*ext_hdr)) {
+    if (input_size < ext_hdr_offset + sizeof(*rthdr) + sizeof(*dst_addr)) {
         return false;
     }