Uses entity bulker to program routes and neighbors during mux
switchover. Mux switchover performance suffers when switching over with
a large number of neighbors on the mux port. This uses the optimization
of programming the neighbors and routes in bulk to avoid sequentially
programming each.

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

bulk switchover feature chages the sai_api calls in switchover flow.
Because of this mux_rollback_ut tests fail. This PR adds bulk operations
to mock_sai_neighbor and mock_sai_api, and adjusts the expected function
calls in mux_rollback_ut.

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

 - using existing add/removeNeighbor functions to do bulker operations.
 - Created addNeighborPost and removeNeighborPost
 - Created addRoutes and removeRoutes to deal with bulk operations
 - Created enableNeighbors and disableNeighbors to handle bulk
 switchover.

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>

Signed-off-by: Nikola Dancejic <ndancejic@microsoft.com>