The NetworkMode "default" is now normalized into the value it
aliases ("bridge" on Linux and "nat" on Windows) by the
ContainerCreate endpoint, the legacy image builder, Swarm's
cluster executor and by the container restore codepath.
builder-next is left untouched as it already uses the normalized
value (ie. bridge).
Going forward, this will make maintenance easier as there's one
less NetworkMode to care about.
Signed-off-by: Albin Kerouanton <albinker@gmail.com>