From Anton Blanchard.  This fixes a couple of Linux Test Project
failures.

- Returns EBUSY if the caller is trying to invalidate memory which is
  covered by a locked vma.

  The open group say:

  [EBUSY]
          Some or all of the addresses in the range starting
          at addr and continuing for len bytes are locked,
          and MS_INVALIDATE is specified.

- Returns EINVAL if the caller specified both MS_SYNC and MS_ASYNC

  [EINVAL]
          The value of flags is invalid.

  and:

          "Either MS_ASYNC or MS_SYNC is specified, but not both."