ovn-docker-driver: Handle "underlay" mode for network-create.
ovn-docker-driver: Handle "underlay" mode for network-create.

Signed-off-by: Gurucharan Shetty <c4089df073b4e0e1342dd7f47682381cc38caa5c@nicira.com>

shettyg/ovn-docker,shettyg/ovn-docker,shettyg/ovn-docker