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