netdev-offload-tc: Fix offload of tunnel key tp_src.

There is no TCA_TUNNEL_KEY_ENC_SRC_PORT in the kernel, so the offload
should not be attempted if OVS_TUNNEL_KEY_ATTR_TP_SRC is requested
by OVS.  Current code just ignores the attribute in the tunnel(set())
action leading to a flow mismatch and potential incorrect datapath
behavior:

  |tc(handler21)|DBG|tc flower compare failed action compare
  ...
  Action 0 mismatch:
  - Expected Action:
  00000010 01 00 00 00 00 00 00 00-00 00 00 00 00 ff 00 11
  00000020 c0 5b 17 c1 00 40 00 00-0a 01 00 6d 0a 01 01 12
  00000050 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  00000060 01 02 80 01 00 18 00 0b-00 00 00 00 00 00 00 00
  ...
 - Received Action:
  00000010 01 00 00 00 00 00 00 00-00 00 00 00 00 ff 00 11
  00000020 00 00 17 c1 00 40 00 00-0a 01 00 6d 0a 01 01 12
  00000050 08 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  00000060 01 02 80 01 00 18 00 0b-00 00 00 00 00 00 00 00
  ...

In the tc_action dump above we can see the difference on the second
line.  The action dumped from a kernel is missing 'c0 5b' - source
port for a tunnel(set()) action on the second line.

Removing the field from the tc_action_encap structure entirely to
avoid any potential confusion.

Note: In general, the source port number in the tunnel(set()) action
is not particularly useful for most tunnels, because they may just
ignore the value.  Specs for Geneve and VXLAN suggest using a value
based on the headers of the inner packet as a source port.
In vast majority of scenarios the source port doesn't actually end
up in the action itself.
Having a mismatch between the userspace and TC leads to constant
revalidation of the flow and warnings in the log.

Fixes: 8f283af ("netdev-tc-offloads: Implement netdev flow put using tc interface")
Reported-at: https://mail.openvswitch.org/pipermail/ovs-discuss/2023-October/052744.html
Reported-by: Vladislav Odintsov <[email protected]>
Acked-by: Eelco Chaudron <[email protected]>
Signed-off-by: Ilya Maximets <[email protected]>

lib/netdev-offload-tc.c

@@ -1627,7 +1627,9 @@ parse_put_flow_set_action(struct tc_flower *flower, struct tc_action *action,
         }
         break;
         case OVS_TUNNEL_KEY_ATTR_TP_SRC: {
-            action->encap.tp_src = nl_attr_get_be16(tun_attr);
+            /* There is no corresponding attribute in TC. */
+            VLOG_DBG_RL(&rl, "unsupported tunnel key attribute TP_SRC");
+            return EOPNOTSUPP;
         }
         break;
         case OVS_TUNNEL_KEY_ATTR_TP_DST: {

lib/tc.h

@@ -213,7 +213,8 @@ enum nat_type {
 struct tc_action_encap {
     bool id_present;
     ovs_be64 id;
-    ovs_be16 tp_src;
+    /* ovs_be16 tp_src;  Could have been here, but there is no
+     * TCA_TUNNEL_KEY_ENC_ attribute for it in the kernel. */
     ovs_be16 tp_dst;
     uint8_t tos;
     uint8_t ttl;