ocfs2: De-magic the in-memory slot map.

The in-memory slot map uses the same magic as the on-disk one.  There is
a special value to mark a slot as invalid.  It relies on the size of
certain types and so on.

Write a new in-memory map that keeps validity as a separate field.  Outside
of the I/O functions, OCFS2_INVALID_SLOT now means what it is supposed to.
It also is no longer tied to the type size.

This also means that only the I/O functions refer to 16bit quantities.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Mark Fasheh <mfasheh@suse.com>
diff --git a/fs/ocfs2/slot_map.h b/fs/ocfs2/slot_map.h
index 5118e89..601c95f 100644
--- a/fs/ocfs2/slot_map.h
+++ b/fs/ocfs2/slot_map.h
@@ -39,6 +39,6 @@
 int ocfs2_slot_to_node_num_locked(struct ocfs2_super *osb, int slot_num,
 				  unsigned int *node_num);
 
-int ocfs2_clear_slot(struct ocfs2_super *osb, s16 slot_num);
+int ocfs2_clear_slot(struct ocfs2_super *osb, int slot_num);
 
 #endif