gianfar: Don't free/request irqs on device reset

Resetting the device (stop_gfar()/startup_gfar()) should
be fast and to the point, in order to timely recover
from an error condition (like Tx timeout) or during
device reconfig.  The irq free/ request routines are just
redundant here, and they should be part of the device
close/ open routines instead.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>