This add support for IGMP Snooping on atheros switches (disabled by default),
which avoids flooding the network with multicast data.
Tested on TL-WDR4300: disabling IGMP Snooping results in multicast flooding
on each specific port, enabling it back again prevents each port from
receiving all multicast packets.
Partially based on: http://patchwork.ozlabs.org/patch/418122/
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
SVN-Revision: 48268
f8d2ec6e9d