NFS: add RPC I/O statistics to /proc/self/mountstats

NFS client now shows various RPC I/O metrics in /proc/self/mountstats.

Test plan:
Mount/umount while doing "cat /proc/self/mountstats", multiple iterations
of connectathon locking suite.  Test with NFS version 2, 3, and 4.
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/inode.c

@@ -26,6 +26,7 @@
 #include <linux/unistd.h>
 #include <linux/sunrpc/clnt.h>
 #include <linux/sunrpc/stats.h>
+#include <linux/sunrpc/metrics.h>
 #include <linux/nfs_fs.h>
 #include <linux/nfs_mount.h>
 #include <linux/nfs4_mount.h>
@@ -728,6 +729,9 @@ static int nfs_show_stats(struct seq_file *m, struct vfsmount *mnt)
 	seq_printf(m, "\n\tbytes:\t");
 	for (i = 0; i < __NFSIOS_BYTESMAX; i++)
 		seq_printf(m, "%Lu ", totals.bytes[i]);
+	seq_printf(m, "\n");
+
+	rpc_print_iostats(m, nfss->client);
 
 	return 0;
 }