core: added field to link sip msg in onsend structure

- to be used when opening an ongoing stream (tcp/tls) connection
core: option to specify whether the send info has to be set before sending out
tls: execute event_route[tls:connection-out]

- done when a new outgoing tls connection is opened
- ongoing work, to allow an option to drop the connection based on
  config decision
auth_db: auth_check() to get the auth header from the used api

- this avoids using a different auth header that might be in the request
  before checking usernames in from/to headers against auth user