appletalk:: da.s_net not copied but assigned to itself in aarp_rcv()

da.s_net was not copied but assigned to itself.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>