mvneta_tx() dereferences skb to get skb->len too late,
as hardware might have completed the transmit and TX completion
could have freed the skb from another cpu.

Fixes: 71f6d1b3 ("net: mvneta: replace Tx timer with a real interrupt")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

(cherry picked from commit 5f478b41)
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>