Fix the radiotap printer to handle the special bits correctly.

Fix the radiotap printer to handle the special bits correctly.

Process bits 29, 30, and 31 in code that's independent of what namespace
we're in:

  If we're switching to the radiotap namespace, reset the bit numbers to
  start back at 0.

  If we're switching to a vendor namespace, get the vendor OUI and
  subspace, and the skip length.

  Keep trace of which namespace we're in.

  If we're *in* a vendor namespace, skip over the data specified by the
  skip length (and reset it, as we've processed all the vendor namespace
  data and, if there's a subsequent bitmap in the same namespace,
  there's nothing more to process.  Use cpack_align_and_reserve() to
  skip that, so we check that we don't go past the end of the packet
  data.

Fixes GitHub tcpdump issue #498.

This removes some bogus errors; update the test output to reflect that.