res_pjsip_endpoint_identifier_ip: Endpoint identifier request URI

Add ability to match against PJSIP request URI.

UserNote: this new feature let users match endpoints based on the
indound SIP requests' URI. To do so, add 'request_uri' to the
endpoint's 'identify_by' option. The 'match_request_uri' option of
the identify can be an exact match for the entire request uri, or a
regular expression (between slashes). It's quite similar to the
header identifer.

Fixes: #599

res/res_pjsip/pjsip_config.xml

@@ -557,6 +557,14 @@
 								endpoint identification.
 								</para>
 							</enum>
+							<enum name="request_uri">
+								<para>Matches the endpoint based on the configured SIP
+								request uri.
+								</para>
+								<para>This method of identification is not configured here
+								but simply allowed by this configuration option.
+								</para>
+							</enum>
 						</enumlist>
 					</description>
 				</configOption>