firewire: net: identify to driver core as "firewire_net", not "net"

On second thought, there is little reason to have driver name differ
from module name.  Therefore, change
    /sys/bus/firewire/drivers/net
    /sys/bus/firewire/devices/fw0.0/driver -> [...]/net
    /sys/module/firewire_net/drivers/firewire:net
to
    /sys/bus/firewire/drivers/firewire_net
    /sys/bus/firewire/devices/fw0.0/driver -> [...]/firewire_net
    /sys/module/firewire_net/drivers/firewire:firewire_net
It is redundant but consistent with firewire-sbp2's recently changed
driver name.

I don't see this anywhere used, so it should not matter either way.

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