- moving state look up outside of PF_LOCK()

- moving state look up outside of PF_LOCK()

this change adds a pf_state_lock rw-lock, which protects consistency
of state table in PF. The code delivered in this change is guarded
by 'WITH_PF_LOCK', which is still undefined. People, who are willing
to experiment and want to run it must do two things:

	- compile kernel with -DWITH_PF_LOCK
	- bump NET_TASKQ from 1 to ... sky is the limit,
	  (just select some sensible value for number of tasks your
	  system is able to handle)

OK bluhm@