This patch fixes a problem that occurs when packets cannot be sent across
the ieee1394 bus and we return NETDEV_TX_BUSY in the net driver "hard start
xmit" routine ether1394_tx. When we return NETDEV_TX_BUSY the stack will
call ether1394_tx again with the same skb. So we need to restore the header
to look like it did before we munged it for xmit over ieee1394.

[Stefan Richter: changed whitespace, deleted a local variable]
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>