firewire: net: adjust net_device ops

The .ndo_tx_timeout callback is currently without function; delete it.
Give .watchdog_timeo a proper time value; lower it to 2 seconds.

Decrease the .tx_queue_len from 1000 (as in Ethernet card drivers) to 10
because we have only 64 transaction labels available, and responders
might have further limits of their AR req contexts.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>