list_for_each_entry_lockless as it has compiler barriers requred
to safely run concurrently with the _rcu list-mutation primitives
such as list_add_rcu().
On Linux list_for_each_entry_rcu has additional diagnostic checks as
compared with list_for_each_entry_lockless which FreeBSD does not
implements, so for us they both are equal.
Also move the macro to linux/rculist.h where it should reside.