util:veth: Create veth device pair by netlink
util:veth: Create veth device pair by netlink

When netlink is supported, use netlink to create veth device pair
rather than 'ip link' command.

Signed-off-by: Shi Lei <79e2d1a953a210f9f0c36cafbe946414d6421d20@massclouds.com>
Reviewed-by: Laine Stump <c23361c43fbf79fed83e8b76173707b083d6caf5@redhat.com>

nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,jfehlig/libvirt,nertpinx/libvirt,nertpinx/libvirt,crobinso/libvirt