util: fix libvirtd startup failure due to netlink error

util: fix libvirtd startup failure due to netlink error

This is part of the solution to the problem detailed in:

  https://bugzilla.redhat.com/show_bug.cgi?id=816465

and further detailed in

  https://www.redhat.com/archives/libvir-list/2012-May/msg00202.htm

A short explanation is included in the comments of the patch itself.

Note that this patch by itself breaks communication between lldpad and
libvirtd, so the other 3 patches in the series must be applied at the
same time as this patch.