A Linux PC is connected with another device over Bluetooth PAN using a
BNEP interface.

Whenever a packet is tried to be sent over the BNEP interface, the
function "bnep_net_xmit()" in "net/bluetooth/bnep/netdev.c" is called.
This function calls "bnep_net_mc_filter()", which checks (if the
destination address is multicast) if the address is set in a certain
multicast filter (&s->mc_filter). If it is not, then it is not sent out.

This filter is only changed in two other functions, found in
net/bluetooth/bnep/core.c": in "bnep_ctrl_set_mc_filter()", which is
only called if a message of type "BNEP_FILTER_MULTI_ADDR_SET" is
received. Otherwise, it is set in "bnep_add_connection()", where it is
set to a default value which only adds the broadcast address to the
filter:

set_bit(bnep_mc_hash(dev->broadcast), (ulong *) &s->mc_filter);

To sum up, if the BNEP interface does not receive any message of type
"BNEP_FILTER_MULTI_ADDR_SET", it will not send out any messages with
multicast destination addresses except for broadcast.

However, in the BNEP specification (page 27 in
http://grouper.ieee.org/groups/802/15/Bluetooth/BNEP.pdf), it is said
that per default, all multicast addresses should not be filtered, i.e.
the BNEP interface should be able to send packets with any multicast
destination address.

It seems that the default case is wrong: the multicast filter should not
block almost all multicast addresses, but should not filter out any.

This leads to the problem that e.g. Neighbor Solicitation messages sent
with Bluetooth PAN over the BNEP interface to a multicast destination
address other than broadcast are blocked and not sent out.

Therefore, in the default case, we set the mc_filter to ~0LL to not
filter out any multicast addresses.
Signed-off-by: Danny Schweizer <danny.schweizer@proofnet.de>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>