Don't restart dhcpd after tweaking pxe_boot related state.
Don't restart dhcpd after tweaking pxe_boot related state.

dhcpd isn't running at this time so invoking dhcpd_makeconf will blow up
the elabinelab setup.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome