Comment 8 for bug 1573272

Ok I've reproduced this by introducing a delay by changing /lib/systemd/system/ifup@.service

-ExecStart=/bin/sh -ec 'ifup --allow=hotplug %I; ifup --allow=auto %I; \
+ExecStart=/bin/sh -ec '/usr/bin/test %I == bond0 && echo found bond0 && sleep 3 ; ifup --allow=hotplug %I; ifup --allow=auto %I; \

that reproduces this by allowing bond0.3000 to complete ifup before bond0 is processed, and when bond0 is ifup'ed it clears bond0.3000's gateway due to bond0 going down and back up.