chan_pjsip: Fix ability to send UPDATE on COLP

When connected_line_method is "invite", we're supposed to determine
if the client can support UPDATE and if it can, send UPDATE instead
of INVITE to avoid the SDP renegotiation.  Not only was pjproject
not setting the PJSIP_INV_SUPPORT_UPDATE flag, we were testing
that invite_tsx wasn't NULL which isn't always the case.

* Updated chan_pjsip/update_connected_line_information to drop the
  requirement that invite_tsx isn't NULL.
* Submitted patch to pjproject sip_inv.c that sets the
  PJSIP_INV_SUPPORT_UPDATE flag correctly.
* Updated pjsip.conf.sample to clarify what happens when "invite"
  is specified.

ASTERISK-27095

Change-Id: Ic2381b3567b8052c616d96fbe79564c530e81560

third-party/pjproject/patches/0070-Set-PJSIP_INV_SUPPORT_UPDATE-correctly-in-pjsip_inv_.patch

@@ -0,0 +1,29 @@
+From 1193681959816effa121c4470748d5faa3a59272 Mon Sep 17 00:00:00 2001
+From: George Joseph <gjoseph@digium.com>
+Date: Thu, 29 Jun 2017 13:42:10 -0600
+Subject: [PATCH] Set PJSIP_INV_SUPPORT_UPDATE correctly in
+ pjsip_inv_verify_request3
+
+pjsip_inv_verify_request3 was setting rem_options when UPDATE was
+detected in the Allow header.  That's just an internal variable and
+doesn't go anywhere.  It's '*options' that needs to be set.
+---
+ pjsip/src/pjsip-ua/sip_inv.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/pjsip/src/pjsip-ua/sip_inv.c b/pjsip/src/pjsip-ua/sip_inv.c
+index fbc8ebe..6db7e6b 100644
+--- a/pjsip/src/pjsip-ua/sip_inv.c
++++ b/pjsip/src/pjsip-ua/sip_inv.c
+@@ -1237,7 +1237,7 @@ PJ_DEF(pj_status_t) pjsip_inv_verify_request3(pjsip_rx_data *rdata,
+ 
+ 	if (i != allow->count) {
+ 	    /* UPDATE is present in Allow */
+-	    rem_option |= PJSIP_INV_SUPPORT_UPDATE;
++	    *options |= PJSIP_INV_SUPPORT_UPDATE;
+ 	}
+ 
+     }
+-- 
+2.9.4
+