fm10k: fix Tx multi-segment frame

fm10k: fix Tx multi-segment frame

In TX side, bit FM10K_TXD_FLAG_LAST in TX descriptor only is set
in the last descriptor for multi-segment packets. But current
implementation didn't set all the fields of TX descriptor, which
will cause descriptors processed now to re-use fields set in last
scroll. If FM10K_TXD_FLAG_LAST bit was set in the last round and
it happened this is not the last descriptor of a multi-segnment
packet, HW will send out the incomplete packet out and leads to
data intergrity issue.

Signed-off-by: Chen Jing D(Mark) <jing.d.chen@intel.com>
Acked-by: Shaopeng He <shaopeng.he@intel.com>
Tested-by: Michael Qiu <michael.qiu@intel.com>
Acked-by: Michael Qiu <michael.qiu@intel.com>