[syslog-ng] IPv6 addresses logged as 127.0.0.1

[Michael Granzow]

When using the template parameter $SOURCEIP, connections originating
from IPv6 addresses are logged as "127.0.0.1".  The following patch
fixes that issue.

Listening on :: on dual-stack hosts will lead to IPv4 connections
being logged in IPv6-mapped format, e.g. ::ffff:10.11.12.13.  This is
not what people usually expect, but it's not wrong.  If desired, the
place to fix that would be g_sockaddr_inet6_format().