btrfs: don't clear CTL bits when trying to release extent state

When trying to release the extent states due to memory pressure we'll
set all the bits except LOCKED, NODATASUM, and DELALLOC_NEW.  This
includes some of the CTL bits, which isn't really a problem but isn't
correct either.  Exclude the CTL bits from this clearing.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>