rculfhash: create dummy nodes directly when create lfht

make cds_lfht_new() can be called earlier(before rcu is initialized
..etc) If caller want to *parallelly* init the dummy nodes with large
init_size, he can use cds_lfht_new()+cds_lfht_resize() combination.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>