We document that an macvlan network with no parent interface is
equivalent to a '--internal' network. But, in this case, an macvlan
network was still configured with a gateway. So, DNS proxying would
be enabled in the internal resolver (and, if the host's resolver
was on a localhost address, requests to external resolvers from the
host's network namespace would succeed).
This change disables configuration of a gateway for a macvlan Endpoint
if no parent interface is specified.
(Note if a parent interface with no external network is supplied as
'-o parent=<dummy>', the gateway will still be set up. Documentation
will need to be updated to note that '--internal' should be used to
prevent DNS request forwarding in this case.)
Signed-off-by: Rob Murray <rob.murray@docker.com>
cd7240f6d9