Draft: Fix internal calls between local SIP endpoints, REF 15092

Sometimes, local calls are not working, resulting in a 401 Unauthenticated error. The issue is reproduced depending on the order of users registration. When the issue is reproduced it can be seen in the Asterisk log that it tries to authenticate the wrong user; an example of the log is here https://project.iopsys.eu/issues/15092 The root cause of this behavior is unclear. The proposed fix is a workaround: it simply validates if the given user matches the one in the incoming authentication header. If not, we mark it as already authenticated, preventing a failure.