bgp: add parameter for site_of_origins to neighbor_add and vrf_add method

added parameter for site_of_origins to neighbor_add and vrf_add method,
and fixed some import error.

Signed-off-by: Hiroshi Yokoi <yokoi.hiroshi@po.ntts.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>