afs: Push the net ns pointer to more places

Push the network namespace pointer to more places in AFS, including the
afs_server structure (which doesn't hold a ref on the netns).

In particular, afs_put_cell() now takes requires a net ns parameter so that
it can safely alter the netns after decrementing the cell usage count - the
cell will be deallocated by a background thread after being cached for a
period, which means that it's not safe to access it after reducing its
usage count.

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

fs/afs/inode.c

@@ -437,7 +437,7 @@ void afs_evict_inode(struct inode *inode)
 		spin_lock(&vnode->server->fs_lock);
 		rb_erase(&vnode->server_rb, &vnode->server->fs_vnodes);
 		spin_unlock(&vnode->server->fs_lock);
-		afs_put_server(vnode->server);
+		afs_put_server(afs_i2net(inode), vnode->server);
 		vnode->server = NULL;
 	}