[APPLETALK]: Fix broadcast bug.

From: Oliver Dawid <oliver@helios.de>

we found a bug in net/appletalk/ddp.c concerning broadcast packets. In 
kernel 2.4 it was working fine. The bug first occured 4 years ago when 
switching to new SNAP layer handling. This bug can be splitted up into a 
sending(1) and reception(2) problem:

Sending(1)
In kernel 2.4 broadcast packets were sent to a matching ethernet device 
and atalk_rcv() was called to receive it as "loopback" (so loopback 
packets were shortcutted and handled in DDP layer).

When switching to the new SNAP structure, this shortcut was removed and 
the loopback packet was send to SNAP layer. The author forgot to replace 
the remote device pointer by the loopback device pointer before sending 
the packet to SNAP layer (by calling ddp_dl->request() ) therfor the 
packet was not sent back by underlying layers to ddp's atalk_rcv().

Reception(2)
In atalk_rcv() a packet received by this loopback mechanism contains now 
the (rigth) loopback device pointer (in K...