[TIPC]: Improved support for Ethernet traffic filtering

This patch simplifies TIPC's Ethernet receive routine to take
advantage of information already present in each incoming sk_buff
indicating whether the packet was explicitly sent to the interface,
has been broadcast to all interfaces, or was picked up because the
interface is in promiscous mode.

This new approach also fixes the problem of TIPC accepting unwanted
traffic through UML's multicast-based Ethernet interfaces (which
deliver traffic in a promiscuous manner even if the interface is
not configured to be promiscuous).

Signed-off-by: Allan Stephens <allan.stephens@windriver.com>
Signed-off-by: Jon Paul Maloy <jon.maloy@ericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>