wifi - Add sepolicy for wifi_perf_diag

wifi_perf_diag is a daemon for wifi performance diagnostic

Ignore-AOSP-First: internal review from here first
Bug: 213117526
Test: wifi_perf_diag is workable
Change-Id: Ie883d79d394333b56026119c71af8c474f564f80
diff --git a/wifi_perf_diag/file_contexts b/wifi_perf_diag/file_contexts
new file mode 100644
index 0000000..a599455
--- /dev/null
+++ b/wifi_perf_diag/file_contexts
@@ -0,0 +1 @@
+/vendor/bin/wifi_perf_diag        u:object_r:wifi_perf_diag_exec:s0