net: fec: add statistics for XDP_TX

The FEC driver supports the statistics for XDP actions except for
XDP_TX before, because the XDP_TX was not supported when adding
the statistics for XDP. Now the FEC driver has supported XDP_TX
since commit f601899e

 ("net: fec: add XDP_TX feature support").
So it's reasonable and necessary to add statistics for XDP_TX.

Signed-off-by: Wei Fang <wei.fang@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>