server/keyset.c, server/keymgmt.c: Variable data limits.

server/keyset.c, server/keymgmt.c: Variable data limits.

The old static data volume limit isn't acceptable when trying to keep up
with LANs (e.g., wireless LANs) or other fast networks.  This change
configures a variable volume limit based on the width of the underlying
block cipher.  (That means it doesn't do anything sensible with stream
ciphers, but as currently implemented in Catacomb they're a bad idea
anyway.)