log/syslog: document if network=="" for Dial, it will connect to local syslog server. Fixes issue 7828.
log/syslog: document if network=="" for Dial, it will connect to local syslog server.
Fixes issue 7828.

LGTM=robert.hencke, iant, bradfitz
R=golang-codereviews, robert.hencke, iant, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/97780045

apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang