The multiprovidernet API extension's definition was rehomed into
neutron-lib with If3367e6a14074a6225bba527e8f7e38c51280f85 and will be
consumed in neutron via I12c15c360f8bf5a45fbe70e5ed1202ef0e7ec0f0
This patch switches the code over to use neutron-lib's multiprovidernet
API definition rather than neutron's extension.
Change-Id: I6803fdf363a674303f21241a59dc6a281c84d433