Rewrite GSS sequence state tracking code

Replace util_ordering.c with a new file util_seqstate.c, implemented
using a bitmap of previously received sequence numbers instead of a
20-element circular queue.  This approach has slightly different
limitations--it can check for replays for values within 64 of the
expected next number, where the old code could check within the range
of the last 20 received numbers regardless of how far apart they are.
The new approach should work as well or better for any realistic
packet reordering scenario.