- Refactor the WFP interface:
  * WinDivert sublayers are created and inserted when the driver is loaded.
  * All WinDivert callouts are installed at the same sublayer.
- Clean-up the implementation of priorities.
- Re-introduce deep copying for SNIFF mode.  This avoids referencing the
  sniffed packets.
- Fix-up the netfilter example:
  * Don't send RSTs to RST/FINs, this can start a RST war.
  * Don't inject ICMP outbound - this may not be a problem despite 1233 errors.