add LACP application

this application provides the simple example of link aggregation using LACP.

the module "lacplib" controls exchange of LACP packets and watches the
status of the slave i/fs.  the status changes if the i/fs went into a
LAG or timeout to exchange LACP occurred.  the module sends a
"EventSlaveStateChanged" event when the status changed.

the module "simple_switch_lacp" is a variation of "simple_switch".
the switch receives the "EventPacketIn" event instead of the
"EventOFPPacketIn" event from the module "lacplib" in order to except
LACP.  when the module received "EventSlaveStateChanged" event, the
module resets flow entries.

to run:
ryu-manager ryu/app/simple_switch_lacp.py

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