mih: Fix some bugs; Add an XXX comment.

  One of the bugs: (2^32) is *not* 2 to the power of 32.

Change-Id: I0875ba5ac37717b778ee9252c7bce8a2ac442158
Reviewed-on: https://code.wireshark.org/review/5132
Reviewed-by: Bill Meier <wmeier@newsguy.com>