add IGMP snooping application

this application provides the simple example of IGMP snooping.

the module "igmplib" mainly offers 2 functions:
- listening on in the IGMP conversation between multicast routers and hosts
- emulating of the querier function of multicast servers
the former operates a switch as a snooping switch and controls transmission of an unnecessary multicasting packet.
the latter realizes the IGMP conversation in the environment without multicast routers.

the module "simple_switch_igmp" is a variation of "simple_switch".
the switch receives the "EventPacketIn" event instead of the "EventOFPPacketIn" event from the module "igmplib" in order to except IGMP.

Signed-off-by: Yuichi Ito <ito.yuichi0@gmail.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>