tinyds: add 'protocol_trace' feature

tinyds: add 'protocol_trace' feature

1. add rules in rule file
ALLOW iface=wl_pointer and msg=motion
ALLOW iface=wl_seat and type=event

2. set environment variables (or default path is given)
$export DS_PROTOCOL_RULE_FILE=/tmp/rule
$export DS_PROTOCOL_TRACE_FILE=/tmp/trace

3. will see protocol logs in trace file
$tail -f /tmp/trace
[1499148.714] Server->Client [PID:25430]wl_seat@7.capabilities(7), cmd: ds-simple-tbm
[1499148.810] Server->Client [PID:25430]wl_seat@7.name("seat0"), cmd: ds-simple-tbm
[1499155.391] Server   [PID:25430] client destroying

Change-Id: I9fff75555d002fa0c25a5f3d61ce31c8d7c0886b