For backward compatibility: if no custom options are provided for the network,
and only a single network is specified, omit the endpoint-configuration
on the client (the daemon will still create it when creating the container)
This fixes an issue on older versions of legacy Swarm, which did not support
`NetworkingConfig.EndpointConfig`.
This was introduced in 5bc09639cc (#1767)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 4d7e6bf629)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>