Preference for Privacy Extensions (RFC3041). <= 0 : disable Privacy Extensions == 1 : enable Privacy Extensions, but prefer public addresses over temporary addresses.
1 : enable Privacy Extensions and prefer temporary addresses over public addresses. Default: 0 (for most devices) -1 (for point-to-point devices and loopback devices)
Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.
source