res_pjsip: Split type=identify to IP address and SIP header matching priorities

The type=identify endpoint identification method can match by IP address
and by SIP header.  However, the SIP header matching has limited
usefulness because you cannot specify the SIP header matching priority
relative to the IP address matching.  All the matching happens at the same
priority and the order of evaluating the identify sections is
indeterminate.  e.g., If you had two type=identify sections where one
matches by IP address for endpoint alice and the other matches by SIP
header for endpoint bob then you couldn't predict which endpoint is
matched when a request comes in that matches both.

* Extract the SIP header matching criteria into its own "header" endpoint
identification method so the user can specify the relative priority of the
SIP header and the IP address matching criteria in the global
endpoint_identifier_order option.  The "ip" endpoint identification method
now only matches by IP address.

ASTERISK-27491

Change-Id: I9df142a575b7e1e3471b7cda5d3ea156cef08095

UPGRADE.txt

@@ -43,19 +43,3 @@ ARI:
 cdr_syslog:
  - The cdr_syslog module is now deprecated and by default it is no longer
    built.
-
-New in 15.0.0:
-
-Build System:
- - '--with-pjproject-bundled' is now the default when running ./configure
-   It can be disabled with '--without-pjproject-bundled'.
-
-Core:
- - Multi-stream support has been added so a channel can have multiple
-   streams of the same type such as audio and video.
-
- - The 'Data Retrieval API' has been removed. This API was not actively
-   maintained, was not added to new modules (such as res_pjsip), and there
-   exist better alternatives to acquire the same information, such as the
-   ARI. As a result, the 'DataGet' AMI action as well as the 'data get'
-   CLI command have been removed.