hiqnet: Simplify code somewhat; Adjust the "names" and display of certain fields.

Specifically: Use proto_tree_add_bitmask() to show the "flags" and
              "categories" bitfields (instead of building the fields
              display "by hand").
              The bitfield display changed as follows:
              - A bitfield with all bits=0 will have a detailed
                dissection tree; (for both 'flags' & 'categories');
              - The 'categories' individual bitfields are now
                displayed as FT_BOOLEAN (not FT_UINT32).

Change-Id: Icd35698aae492b81b340d08030e6a1563f1640ae
Reviewed-on: https://code.wireshark.org/review/5266
Reviewed-by: Bill Meier <wmeier@newsguy.com>