Allow installd to measure size of dexopt links.

avc: denied { getattr } for path="/data/dalvik-cache/arm64/system@framework@boot-core-libart.oat" dev="sda35" ino=1581062 scontext=u:r:installd:s0 tcontext=u:object_r:dalvikcache_data_file:s0 tclass=lnk_file permissive=0

Test: builds, boots, quota stats match manual stats
Bug: 27948817
Change-Id: I65fb581a4732e03c46ac705f6693080c5f3be184