This commit will allow the host_discovery_packet_in_handler to ignore invalid cfm packets. Ryu will fail to parse cfm packets with an interval of 0 -- We discovered this when one of our systems sent cfm packets with an interval of 0. Signed-off-by: Evan Gray <evanscottgray@gmail.com> Reviewed-by: Iwase Yusuke <iwase.yusuke0@gmail.com> Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>