Merge branch 'packet-fanout-unique-id'

Mike Maloney says:

====================
packet: Add option to create new fanout group with unique id.

Fanout uses a per net global namespace. A process that intends to create a
new fanout group can accidentally join an existing group. It is
not possible to detect this.

Add a socket option to specify on the first call to
setsockopt(..., PACKET_FANOUT, ...) to ensure that a new group is created.
Also add tests.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>