net: define the TSO header size in net/tso.h

The TSO header size was defined in many drivers. Factorize the code and
define its size in net/tso.h.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -281,9 +281,6 @@
  */
 #define MVNETA_RSS_LU_TABLE_SIZE	1
 
-/* TSO header size */
-#define TSO_HEADER_SIZE 128
-
 /* Max number of Rx descriptors */
 #define MVNETA_MAX_RXD 128