Bug#609648: Don't use DHCP on point-to-point links
[More a bug to remind myself for the future than anything else]
I'm not 100% sure of the validity of this, but I *think* that it's not
appropriate to run DHCP over a pointopoint link like PLIP, SLIP, etc.
(Whether those should even bother to be supported any more is a whole other
I need to research this further, to see if it is actually permitted, before
making the (fairly minor) changes to not run DHCP on the link.