Allow the xdm_t domain to enter all the gkeyringd ones

During the opening of the session, the pam_gnome_keyring module is
starting the daemon in the gkeyringd user domain, allow xdm_t to
transition to it.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=742966

policy/modules/services/xserver.te

@@ -523,6 +523,10 @@ optional_policy(`
 	')
 ')
 
+optional_policy(`
+	gnome_spec_domtrans_all_gkeyringd(xdm_t)
+')
+
 optional_policy(`
 	# Talk to the console mouse server.
 	gpm_stream_connect(xdm_t)