New message to elect a new master.

When a master controller dies, a new master is elected at RFMonitor and
it is to be informed to the rfproxy and inturn all the devices. So a new
message type ELECT_MASTER is created that will be used by RFMonitor to
inform the rfproxy.

Signed-off-by: Srijan Mishra <srijan23mishra@gmail.com>