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/private/file_contexts b/private/file_contexts
index 20ef9b8..2350a7c 100644
--- a/private/file_contexts
+++ b/private/file_contexts
@@ -716,6 +716,7 @@
 /data/misc/vpn(/.*)?            u:object_r:vpn_data_file:s0
 /data/misc/wifi(/.*)?           u:object_r:wifi_data_file:s0
 /data/misc_ce/[0-9]+/wifi(/.*)? u:object_r:wifi_data_file:s0
+/data/misc/wifi/mainline_supplicant(/.*)?  u:object_r:mainline_supplicant_data_file:s0
 /data/misc/wifi/sockets(/.*)?   u:object_r:wpa_socket:s0
 /data/misc/wifi/sockets/wpa_ctrl.*   u:object_r:system_wpa_socket:s0
 /data/misc/vold(/.*)?           u:object_r:vold_data_file:s0