Make boolean bitmask type 64-bit wide

There are protocols out there that have 64-bit wide bit mask fields, so
make the internal representation and bitfield decoders 64-bit aware.

For this, the ws_ctz() fallback and bits_count_ones() have to be tweaked
slightly.

Change-Id: I19237b954a69c9e6c55864f281993c1e8731a233
Reviewed-on: https://code.wireshark.org/review/4158
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>