odp-execute: Fix length checking while executing check_pkt_len action.

If dp-packet contains l2 padding or cutlen was applied to it, size will
be larger than the actual size of a payload and action will work
incorrectly.

Ex. Padding could be added during miniflow_extract() if detected.

Fixes: 5b34f8fc3b ("Add a new OVS action check_pkt_larger")
Reported-by: Miroslav Kubiczek <miroslav.kubiczek@adaptivemobile.com>
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2020-May/050157.html
Acked-by: Dumitru Ceara <dceara@redhat.com>
Acked-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

lib/odp-execute.c

@@ -761,10 +761,11 @@ odp_execute_check_pkt_len(void *dp, struct dp_packet *packet, bool steal,
 
     const struct nlattr *a;
     struct dp_packet_batch pb;
+    uint32_t size = dp_packet_get_send_len(packet)
+                    - dp_packet_l2_pad_size(packet);
 
     a = attrs[OVS_CHECK_PKT_LEN_ATTR_PKT_LEN];
-    bool is_greater = dp_packet_size(packet) > nl_attr_get_u16(a);
-    if (is_greater) {
+    if (size > nl_attr_get_u16(a)) {
         a = attrs[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER];
     } else {
         a = attrs[OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL];