OK i got it working i had to edit /etc/default/mediatomb
ssh to the core or from the core
type: sudo nano /etc/default/mediatomb
scroll to them bottom and look for INTERFACE="eth0" and then change it to INTERFACE="eth1"
the press Ctrl c to save and then Ctrl and x to exit
then reboot the core.
Maybe we should create a script so that when you click swap interfaces in webadmin it will change this automatically