Mfp4 CH=177255:

  Resort the CURVNET_SET* macros in the non-VNET_DEBUG case to match
  the call order of the VNET_DEBUG case.

  Add the VNET_ASSERT() to the non-VNET_DEBUG case as well so that
  INVARIANTS will still catch problems.

  Sponsored by: The FreeBSD Foundation
  Sponsored by: CK Software GmbH
  Reviewed by:  jhb