bfdd: Some interfaces don't have mac addresses

bfdd: Some interfaces don't have mac addresses

When an interface does not have a mac address, don't
try to retrieve the mac address ( for it to just fail ).

Example interface:
sharpd@eva [2]> ip link show tun100
21: tun100@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1480 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/ipip 192.168.119.224 peer 192.168.119.120

Let's just notice that there is a NOARP flag and abort the call.

Fixes: #11733
Signed-off-by: Donald Sharp <sharpd@nvidia.com>