Add a missing session supplement unregistration in chan_pjsip for ACKs.

(closes issue ASTERISK-22453)
Reported by: Corey Farrell
Patches:
	chan_pjsip_session_unregister_supplement.patch uploaded by Corey Farrell (license 5909)
........

Merged revisions 399531 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@399533 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_pjsip.c

@@ -2122,6 +2122,7 @@ static int unload_module(void)
 
 	ast_sip_session_unregister_supplement(&chan_pjsip_supplement);
 	ast_sip_session_unregister_supplement(&pbx_start_supplement);
+	ast_sip_session_unregister_supplement(&chan_pjsip_ack_supplement);
 
 	ast_custom_function_unregister(&chan_pjsip_dial_contacts_function);
 	ast_channel_unregister(&chan_pjsip_tech);