crash_dump_fallback: allow dumpstate:pipe_file write.

It appears that selinux requires the write permission to receive
a writable pipe from dumpstate, for unclear reasons. Add the permission
for now.

Bug: http://b/62297059
Test: dumpstate
Change-Id: I0f25682177115aacd5c2203ddc0008228b0380ad

public/te_macros

@@ -459,7 +459,8 @@ userdebug_or_eng(`
 ')
 allow $1 anr_data_file:file append;
 allow $1 dumpstate:fd use;
-allow $1 dumpstate:fifo_file append;
+# TODO: Figure out why write is needed and remove.
+allow $1 dumpstate:fifo_file { append write };
 allow $1 tombstoned:unix_stream_socket connectto;
 allow $1 tombstoned:fd use;
 allow $1 tombstoned_crash_socket:sock_file write;