[AF_PACKET]: Add option to return orig_dev to userspace.

Add a packet socket option to allow the orig_dev index to be returned
to userspace when passing traffic through a decapsulated device, such
as the bonding driver.

This is very useful for layer 2 traffic being able to report which
physical device actually received the traffic, instead of having the
encapsulating device hide that information.

The new option is called PACKET_ORIGDEV.

Signed-off-by: Peter P. Waskiewicz Jr. <peter.p.waskiewicz.jr@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>