nfsd: add trace events

For now just a few simple events to trace the layout stateid lifetime, but
these already were enough to find several bugs in the Linux client layout
stateid handling.

Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/fs/nfsd/trace.c b/fs/nfsd/trace.c
new file mode 100644
index 0000000..82f8907
--- /dev/null
+++ b/fs/nfsd/trace.c
@@ -0,0 +1,5 @@
+
+#include "state.h"
+
+#define CREATE_TRACE_POINTS
+#include "trace.h"