Reduce in_pcbinfo_init() by two params. No users supply any flags to this
function (they used to say UMA_ZONE_NOFREE), so flag parameter goes away.
The zone_fini parameter also goes away. Previously no protocols (except
divert) supplied zone_fini function, so inpcb locks were leaked with slabs.
This was okay while zones were allocated with UMA_ZONE_NOFREE flag, but now
this is a leak. Fix that by suppling inpcb_fini() function as fini method
for all inpcb zones.