mrtg: add 2.17.4

- The Multi Router Traffic Grapher
- You have a router, you want to know what it does all day long?
- Then MRTG is for you. It will monitor SNMP network devices and draw
- pretty pictures showing how much traffic has passed through each interface.
Merge pull request #5239 from robberer/pkgs/mrtg

mrtg: add 2.17.4