After the TX sgl is expanded we need to explicitly mark end of data
at the last buffer that contains data.

Changes in v2
 - use type 'bool' and true/false for 'mark'.
Signed-off-by: NTadeusz Struk <tadeusz.struk@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>