Fixes #5775: Correct AIX log parsing (Strip 'Message forwarded from <hos...

...tname>' header)

Ticket: http://www.rudder-project.org/redmine/issues/5775

To be merged in 2.10
i'm a bit concerned about this. regex are quite inefficient in rsyslog, and here we are effectively doubling the load
couldn't we simply drop all rudder and from .*: rudder: to lighten the load ?