Reorder LOCALLOCK structure members to compact the size
Save 8 bytes (on x86-64) by filling up padding holes.
Author: Takayuki Tsunakawa <tsunakawa.takay@jp.fujitsu.com>
Discussion: https://www.postgresql.org/message-id/
20190219001639.ft7kxir2iz644alf@alap3.anarazel.de