Define policy for /proc/uid_procstat/set.

New procfs file written by the system_server to communicate fg/bg
state of UIDs to switch the statistics counter sets used.

avc: denied { write } for name="set" dev="proc" ino=4026531862 scontext=u:r:system_server:s0 tcontext=u:object_r:proc:s0 tclass=file permissive=1

Test: builds, boots, counter sets updated
Bug: 34360629
Change-Id: I2efbfbba9e73f50ce50a80a3dffd3b14fa55c048
diff --git a/private/genfs_contexts b/private/genfs_contexts
index f701685..6386101 100644
--- a/private/genfs_contexts
+++ b/private/genfs_contexts
@@ -32,6 +32,7 @@
 genfscon proc /tty/drivers u:object_r:proc_tty_drivers:s0
 genfscon proc /uid_cputime/show_uid_stat u:object_r:proc_uid_cputime_showstat:s0
 genfscon proc /uid_cputime/remove_uid_range u:object_r:proc_uid_cputime_removeuid:s0
+genfscon proc /uid_procstat/set u:object_r:proc_uid_procstat_set:s0
 genfscon proc /zoneinfo u:object_r:proc_zoneinfo:s0
 
 # selinuxfs booleans can be individually labeled.