bcachefs: Fix lock ordering under traverse_all()

bcachefs: Fix lock ordering under traverse_all()

traverse_all() traverses btree paths in sorted order, so it should never
see transaction restarts due to lock ordering violations. But some code
in __bch2_btree_path_upgrade(), while necessary when not running under
traverse_all(), was causing some confusing lock ordering violations -
disabling this code under traverse_all() will let us put in some more
assertions.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>