netmgrd: Allow netmgrd to set xlat property

Fix the following denial

init: avc:  denied  { set } for property=persist.net.doxlat
scontext=u:r:netmgrd:s0 tcontext=u:object_r:default_prop:s0
tclass=property_service

CRs-Fixed: 978703
Change-Id: Ifa91d92ee82a29fa3a4a47a6e94dd9152b47e0e5