BZ #1157819: Set DEFROUTE=no on all interfaces by default

https://bugzilla.redhat.com/show_bug.cgi?id=1157819

Only set DEFROUTE=yes on the gateway interface, and ensure that all other
interfaces have DEFROUTE=no
Merge pull request #107 from bcrochet/bz/1157819

BZ #1157819: Set DEFROUTE=no on all interfaces by default