dpaa_eth: NETIF_F_LLTX requires to do our own update of trans_start

As txq_trans_update() only updates trans_start when the lock is held,
trans_start does not get updated if NETIF_F_LLTX is declared.

Signed-off-by: Madalin Bucur <madalin.bucur@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>