BBSIM change to cli command and event mechanism when sending igmp messages

In BBSIM sending igmp join/leave messages are done using event mechanism. This will be disabled due to performance issues and be replaced by invoking associated functions using go-routine. 

Optional vlan id parameter is going to be added to bbsimctl onu igmp command to support multiple vlans.

Mandatory uni id is going to be added to bbsimctl onu igmp command when sending igmp join/leave messages in order not to send messages through all UNIs at once.