AST-2018-008: Fix enumeration of endpoints from ACL rejected addresses.

AST-2018-008: Fix enumeration of endpoints from ACL rejected addresses.

When endpoint specific ACL rules block a SIP request they respond with a
403 forbidden.  However, if an endpoint is not identified then a 401
unauthorized response is sent.  This vulnerability just discloses which
requests hit a defined endpoint.  The ACL rules cannot be bypassed to gain
access to the disclosed endpoints.

* Made endpoint specific ACL rules now respond with a 401 unauthorized
which is the same as if an endpoint were not identified.  The fix is
accomplished by replacing the found endpoint with the artificial endpoint
which always fails authentication.

ASTERISK-27818

Change-Id: Icb275a54ff8e2df6c671a6d9bda37b5d732b3b32