afs: Add stats for data transfer operations

Add statistics to /proc/fs/afs/stats for data transfer RPC operations.  New
lines are added that look like:

	file-rd : n=55794 nb=10252282150
	file-wr : n=9789 nb=3247763645

where n= indicates the number of ops completed and nb= indicates the number
of bytes successfully transferred.  file-rd is the counts for read/fetch
operations and file-wr the counts for write/store operations.

Note that directory and symlink downloading are included in the file-rd
stats at the moment.

Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/write.c

@@ -356,6 +356,12 @@ found_key:
 	}
 
 	switch (ret) {
+	case 0:
+		afs_stat_v(vnode, n_stores);
+		atomic_long_add((last * PAGE_SIZE + to) -
+				(first * PAGE_SIZE + offset),
+				&afs_v2net(vnode)->n_store_bytes);
+		break;
 	case -EACCES:
 	case -EPERM:
 	case -ENOKEY: