Fix 'server_default' parameter usage in models

In ml2 models parameter 'default' is used for vnic_type, profile and
vif_details, but in migrations 27cc183af192_ml2_vnic_type,
157a5d299379_ml2_binding_profile and
50d5ba354c23_ml2_binding_vif_details is used 'server_default' parameter.
Usage 'default' and 'server_default' should be equal in models and
migration. So models in models is added 'server_default' parameter.

Partial-bug: #1295539

Change-Id: If6a17f381d2550daf64916ad3c1b120f41406d56
Merge "Fix 'server_default' parameter usage in models"