If the user specified lxc.net.[i].veth.pair attribute to request that the host
side of a veth pair be given a specific name let's log it at the trace level.
Otherwise, if the user didn't not specify lxc.net.[i].veth.pair veth_attr.veth1
will contain the name of the host side veth device.
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>