Make protocol parsing more faster.

Use named constants for every rpc code, instead of string representation
of rpc code.
It looks like: msg.id == RPC_CHUNK (older msg.id ==
PROTOCOL_LIST.index("rpc::chunk")). In test app it gives perfomance boost
near 10%.
Move disown timer to properly handler.

Restart disown timer every heartbeat properly. It avoid situation,
when eventloop doesn't stop on EPIPE.