logger: add hostname to rfc3164 message

This makes the obsolete protocol a little bit more compliant with the
internet standard, but few should care now when we have rfc5424 support,
and rfc3164 feels broken.  For example it requires hostname to be not
fully qualified, which is hard to understand, and should make users to
prefer the new protocol.

Reported-by: Frank Thilo <thilo@unix-ag.org>
Bug-Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=705217
CC: Andreas Henriksson <andreas@fatal.se>
Signed-off-by: Sami Kerola <kerolasa@iki.fi>