logger: support for logging to UDP socket / remote syslog server

logger: support for logging to UDP socket / remote syslog server

It adds the ability to logger to log a message to a udp socket.  The -n option
followed by the hostname of the remote host is mandatory to do this.  The
optional -P option can be used to change the UDP destination port (default
514).  The function udpopenlog is used to open the udp socket. After that
everything works in almost the same way like it does when logging to a UNIX
socket.

Signed-off-by: Josef Wuebbels <josef.wuebbels@mtu.de>