netdev-linux-private: fix max length to be 16 bits

The dp_packet length is limited to 16 bits, so document that
and fix the length value accordingly.

Fixes: 29cf9c1 ("userspace: Add TCP Segmentation Offload support")
Signed-off-by: Flavio Leitner <fbl@sysclose.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>

lib/netdev-linux-private.h

@@ -38,7 +38,8 @@
 
 struct netdev;
 
-#define LINUX_RXQ_TSO_MAX_LEN 65536
+/* The maximum packet length is 16 bits */
+#define LINUX_RXQ_TSO_MAX_LEN 65535
 
 struct netdev_rxq_linux {
     struct netdev_rxq up;