MT#62756 CSC now sends Referred-By with callee local data in blind xfer

CSC-UI has been changed so that, during a blind transfer, the
Referred-By header is customized with local identity URI.
Without this customisation, jssip puts blindly the subscriber username
which is not always what kamailio proxy expects.

Having correct Referred-By header is important because kamailio proxy
uses this header in order to identify the transferor in a blind transfer call.
In particular, kamailio proxy checks if Referred-By matches custom header
P-Xfer-Firstcall-Callee-To, in this case B is recogized as transferor.

Change-Id: If149b34c16a5dc13116f8fea9a6d8046498753cd

src/api/ngcp-call.js

@@ -458,8 +458,12 @@ export function callBlindTransfer (numberToTransfer) {
             }
         }
         try {
+            const uriString = `Referred-By: <sip:${rtcSession.local_identity.uri.user}@${rtcSession.local_identity.uri.host}>`
             rtcSession.refer(numberToTransfer, {
-                eventHandlers
+                eventHandlers,
+                extraHeaders: [
+                    uriString
+                ]
             })
         } catch (err) {
             reject(err)