Dragan Dosen 1322d09a6f MEDIUM: logs: add support for RFC5424 header format per logger
The function __send_log() iterates over senders and passes the header as
the first vector to sendmsg(), thus it can send a logger-specific header
in each message.

A new logger arguments "format rfc5424" should be used in order to enable
RFC5424 header format. For example:

    log 10.2.3.4:1234 len 2048 format rfc5424 local2 info
2015-09-28 14:01:27 +02:00
..
2015-09-21 20:57:12 +02:00
2009-01-25 13:49:53 +01:00
2015-07-10 16:30:08 +02:00