* Require explicit table creation before use on kernel side.

* Require explicit table creation before use on kernel side.
* Add resize callbacks for upcoming table-based algorithms.

Kernel changes:
* s/ipfw_modify_table/ipfw_manage_table_ent/
* Simplify add_table_entry(): make table creation a separate piece of code.
  Do not perform creation if not in "compat" mode.
* Add ability to perform modification of algorithm state (like table resize).
  The following callbacks were added:
 - prepare_mod (allocate new state, without locks)
 - fill_mod (UH_WLOCK, copy old state to new one)
 - modify (UH_WLOCK + WLOCK, switch state)
 - flush_mod (no locks, flushes allocated data)
 Given callbacks are called if table modification has been requested by add or
   delete callbacks. Additional u64 tc->'flags' field was added to pass these
   requests.
* Change add/del table ent format: permit adding/removing multiple entries
   at once (only 1 supported at the moment).

Userland changes:
* Auto-create tables with warning