ARP replies may/do contain two MAC addresses when using iputils's
arping so we have to use the first one because it's always the "From"
address - which is what we want.
Thanks to Stefan Knoblich <s.knoblich@axsentis.de> for the fixed pattern.
Reported-by: cl@exomail.to
X-Gentoo-Bug: 379181
X-Gentoo-Bug-URL: https://bugs.gentoo.org/379181
645bbf2e0f