As expected, Ken Oberkfell has been hired as manager of the Mets’ new Triple-A affiliate in Buffalo. The Bisons will formally announce Oberkfell at a news conference in Buffalo next Tuesday. “Obie,” who has managed in the Mets’ system before, served as their first-base coach at the major-league level this summer after Jerry Manuel replaced Willie Randolph but was not retained in that role once Manuel’s interim tag was removed.