[moblab] Fix issue with network interface detection.

find_network_interfaces_by_ip_addr can be called twice if the WAN is
slow to get a IP address.

The first call has the side effect of setting the interface for the LAN to
be the first interface.

On each call to find_network_interfaces_by_ip_addr ensure that the WAN
and LAN interfaces are initialized to empty.

TEST=local moblab testing

Change-Id: Idfd8d498f3bac050948917ad339aaa8d74d940f3
Reviewed-on: https://chromium-review.googlesource.com/1544966
Commit-Ready: Keith Haddow <haddowk@chromium.org>
Tested-by: Keith Haddow <haddowk@chromium.org>
Reviewed-by: Matt Mallett <mattmallett@chromium.org>
1 file changed