[tcplp] TCP support on 15.4 (#8590) (#8593)

This commit is fix to avoid dual processing on single TCP packet,
added fix which restricts TCP packet to pass from opentghread
stack. These changes are applicable only when openthread TCP stack is
used and it is implemented under feature flag -
OPENTHREAD_CONFIG_TCP_ENABLE

src/core/net/ip6.cpp

@@ -1062,6 +1062,15 @@ Error Ip6::ProcessReceiveCallback(Message           &aMessage,
             break;
         }
 
+#if OPENTHREAD_CONFIG_TCP_ENABLE
+        // Do not pass TCP message to avoid dual processing from both openthread and POSIX tcp stacks
+        case kProtoTcp:
+        {
+            error = kErrorNoRoute;
+            goto exit;
+        }
+#endif
+
         default:
             break;
         }