prefix pf_state_key and pf_state_item struct bits to make them more unique.

prefix pf_state_key and pf_state_item struct bits to make them more unique.

this makes searching for the struct members easier, which in turn
makes tweaking code around them a lot easier too. sk_refcnt in
particular would have been a lot nicer to fiddle with than just
refcnt because pf_state structs also have a refcnt, which is annoying.

tweaks and ok sashan@
reads ok kn@