device: drop rp_filter handling
After commit b1082aa9 (device: disable rp_filter handling) drop the now unused code. https://bugzilla.redhat.com/show_bug.cgi?id=1651097
After commit b1082aa9 (device: disable rp_filter handling) drop the now unused code. https://bugzilla.redhat.com/show_bug.cgi?id=1651097