Add neverallow rule for set_context_mgr.

Resubmission of commit: 76f3fe33

Removed conflicting rule from unconfined domain.

Change-Id: I3e6da8922ebf636f1cd8ceefea4291d043a28ab7

domain.te

@@ -329,3 +329,6 @@ neverallow { domain -recovery } system_block_device:blk_file write;
 
 # No domains other than install_recovery or recovery can write to recovery.
 neverallow { domain -install_recovery -recovery } recovery_block_device:blk_file write;
+
+# Only servicemanager should be able to register with binder as the context manager
+neverallow { domain -servicemanager } *:binder set_context_mgr;

unconfined.te

@@ -90,4 +90,4 @@ allow unconfineddomain contextmount_type:notdevfile_class_set r_file_perms;
 allow unconfineddomain node_type:node *;
 allow unconfineddomain netif_type:netif *;
 allow unconfineddomain domain:peer recv;
-allow unconfineddomain { domain -init }:binder { call transfer set_context_mgr };
+allow unconfineddomain { domain -init }:binder { call transfer };