restapi: Remove restriction of vnic profile's network

The schema shouldn't restrict the minimal occurrences
of the vnic profile's network property.

Change-Id: Id17697e1e87c7240bec85056896d8151c39667c8
Bug-Url: https://bugzilla.redhat.com/1031925
Signed-off-by: Moti Asayag <masayag@redhat.com>