I have a heavy forwarder running 6.4.1 on CentOS 7 with 2 nics on seperate subnets (data and mgt) that won't communicate on port 8089.
In a netstat I can see that 8089 is listening but no comms.
When I disable one of the interface, everything works fine.
Guessing that splunk is confused about what IP it should be using. I would try setting the IP for interface that you want use by setting SPLUNK_BINDIP= in the splunk-launch.conf.
Note that this conf file is not in apps but rather $SPLUNK_HOME/etc/splunk-launch.conf.
Double check the spec, http://docs.splunk.com/Documentation/Splunk/latest/Admin/Splunk-launchconf, for syntax.
Hope this helps!