sepolicy: allow zygote to use ashmem fds

Ashmem FD selinux labels have recently been changed (aosp/1127917) from
"ashmemd" to the label of the whichever process opens the fd, which
resulted in the following denial:

avc: denied { use } for
path="/dev/ashmemf5dc2dbf-d1e7-457e-b694-93c84704135e" dev="tmpfs"
ino=18972 ioctlcmd=0x7704 scontext=u:r:zygote:s0
tcontext=u:r:system_server:s0 tclass=fd permissive=1

Test: m selinux_policy
Change-Id: I4880420014bda21cd4f83e3d6190c3cfaa76822f
diff --git a/private/zygote.te b/private/zygote.te
index cf5a7a3..66e14b3 100644
--- a/private/zygote.te
+++ b/private/zygote.te
@@ -146,6 +146,9 @@
 # ingore spurious denials
 dontaudit zygote self:global_capability_class_set sys_resource;
 
+# Allow zygote to use ashmem fds from system_server.
+allow zygote system_server:fd use;
+
 ###
 ### neverallow rules
 ###