Add THREAD_PID_OFFSET to tracepoint arguments that pass a TID to userland.

Add THREAD_PID_OFFSET to tracepoint arguments that pass a TID to userland.

Bring these values in sync with the `tid' builtin which already include
the offset.  This is necessary to build script comparing them, like:

tracepoint:sched:enqueue
{
@ts[arg0] = nsecs;
}

tracepoint:sched:on__cpu
/@ts[tid]/
{
latency = nsecs - @ts[tid];
}

Discussed with and ok bluhm@