llist: llist_add() can use llist_add_batch()

llist: llist_add() can use llist_add_batch()

llist_add(new, head) can simply use llist_add_batch(new, new, head),
no need to duplicate the code.

This obviously uninlines llist_add() and to me this is a win. But we
can make llist_add_batch() inline if this is desirable, in this case
gcc can notice that new_first == new_last if the caller is llist_add().

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Andrey Vagin <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Cc: David Howells <[email protected]>
Cc: Huang Ying <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Al Viro <[email protected]>