tracing: move tgid out of generic entry and into userstack

The userstack trace required the recording of the tgid entry.
Unfortunately, it was added to the generic entry where it wasted
4 bytes of every entry and was only used by one entry.

This patch moves it out of the generic field and moves it into the
only user (userstack_entry).

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5c75dee..1a37da2 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -886,7 +886,6 @@
 
 	entry->preempt_count		= pc & 0xff;
 	entry->pid			= (tsk) ? tsk->pid : 0;
-	entry->tgid			= (tsk) ? tsk->tgid : 0;
 	entry->flags =
 #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT
 		(irqs_disabled_flags(flags) ? TRACE_FLAG_IRQS_OFF : 0) |
@@ -1068,6 +1067,7 @@
 		return;
 	entry	= ring_buffer_event_data(event);
 
+	entry->tgid		= current->tgid;
 	memset(&entry->caller, 0, sizeof(entry->caller));
 
 	trace.nr_entries	= 0;