MFC r343772, r343867

MFC r343772, r343867

netmap: refactor logging macros and pipes

Changelist:
    - Replace ND, D and RD macros with nm_prdis, nm_prinf, nm_prerr
      and nm_prlim, to avoid possible naming conflicts.
    - Add netmap_krings_mode_commit() helper function and use that
      to reduce code duplication.
    - Refactor pipes control code to export some functions that
      can be reused by the veth driver (on Linux) and epair(4).
    - Add check to reject API requests with version less than 11.
    - Small code refactoring for the null adapter.