Have atalk_route_packet() return NET_RX_SUCCESS not NET_XMIT_SUCCESS

atalk_route_packet() returns NET_RX_DROP if it's call to
aarp_send_ddp() returns NET_XMIT_DROP. If aarp_send_ddp() returns
anything else atalk_route_packet() should return NET_RX_SUCCESS, not
NET_XMIT_SUCCESS.

Signed-off-by: Mark Smith <markzzzsmith@yahoo.com.au>
Signed-off-by: David S. Miller <davem@davemloft.net>