Breakout BTRFS_SETGET_FUNCS into a separate C file, the inlines were too big.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/tree-defrag.c b/fs/btrfs/tree-defrag.c
index d23216a..0d1a1be 100644
--- a/fs/btrfs/tree-defrag.c
+++ b/fs/btrfs/tree-defrag.c
@@ -239,7 +239,7 @@
 	for (i = 0; i <= orig_level; i++) {
 		if (path->nodes[i]) {
 			free_extent_buffer(path->nodes[i]);
-			path->nodes[i] = 0;
+			path->nodes[i] = NULL;
 		}
 	}
 out: