TT#70068 Add new header to MWI SIP message.

- new header P-NGCP-MWI-Id, that contains the internal
  NGCP message id and needed to distinguish new/old
  messages order within a subscriber to perform selec-
  tive messages handling.

Change-Id: I21556b1ced05baac8f373c2cd15ca63ae45e2c02

mwi.sip

@@ -9,7 +9,7 @@ Event: message-summary
 User-Agent: Sipwise NGCP Application Server
 Content-Type: application/simple-message-summary
 Content-Length: $BODYLEN$
-
+$MWI_ID$
 $BODY_MW$
 $BODY_VM$
 

vmnotify

@@ -288,6 +288,7 @@ sub main {
         ($data{user}, $data{domain}) = get_user_domain($data{mailbox});
         my $etag = get_etag($data{user}, $data{domain});
         my $sipifmatch = defined $etag ? "SIP-If-Match: $etag" : "STRIP";
+        my $mwiid = $data{msgnum} ge 0 ? "P-NGCP-MWI-Id: $data{msgnum}\n": "";
 
         my %macros = (
             body_mw => "Messages-Waiting: ". ($data{new} ? "yes" : "no"),
@@ -297,6 +298,7 @@ sub main {
             user    => $data{user},
             domain  => $data{domain},
             sipifmatch => $sipifmatch,
+            mwi_id => $mwiid,
         );
 
         send_mwi_notify(\%macros);