Introduce Selinux policies for the mainline supplicant.

Aside from binder access, supplicant requires some
networking capabilities in order to work as expected.

Bug: 365585450
Test: Manual test - retrieve the mainline supplicant
      binder in frameworks/base, and call a test
      method using its AIDL interface
Change-Id: Id76fe09b2ecae758ed93b92d92020d45f19d2501
diff --git a/apex/com.android.wifi-file_contexts b/apex/com.android.wifi-file_contexts
index f3a65d4..2355fca 100644
--- a/apex/com.android.wifi-file_contexts
+++ b/apex/com.android.wifi-file_contexts
@@ -1 +1,2 @@
 (/.*)?                u:object_r:system_file:s0
+/bin/wpa_supplicant_mainline       u:object_r:wifi_mainline_supplicant_exec:s0