myri10ge: fix an incorrect free for skb in myri10ge_sw_tso

All remaining skbs should be released when myri10ge_xmit fails to
transmit a packet. Fix it within another skb_list_walk_safe.

Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>