systemd: add siaddr to lease options

This is so that we end up with a next-server option analogous to what
dhclient helper sends us. Dracut uses this for networked boots.
18 jobs for lr/siaddr in 112 minutes and 35 seconds (queued for 1 minute and 30 seconds)
latest
Status Job ID Name Coverage
  Test
passed #902768
allowed to fail
checkpatch

00:00:53

manual #902774
allowed to fail manual
t_centos:7.5.1804
passed #902775
t_centos:7.6.1810

00:20:15

passed #902781
t_debian:10

00:20:26

passed #902780
t_debian:9

00:19:08

passed #902783
t_debian:sid

00:20:50

manual #902782
allowed to fail manual
t_debian:testing
manual #902769
allowed to fail manual
t_fedora:28
passed #902770
t_fedora:29

00:26:30

passed #902771
t_fedora:30

00:32:53

passed #902772
t_fedora:31

00:27:15

manual #902773
allowed to fail manual
t_fedora:rawhide
passed #902776
t_ubuntu:16.04

00:17:48

passed #902777
t_ubuntu:18.04

00:19:19

manual #902779
allowed to fail manual
t_ubuntu:devel
manual #902778
allowed to fail manual
t_ubuntu:rolling
 
  External
failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/858/

failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/858/

06:03:32