pf: Fix deadlock with route-to

If a locally generated packet is routed (with route-to/reply-to/dup-to) out of
a different interface it's passed through the firewall again. This meant we
lost the inp pointer and if we required the pointer (e.g. for user ID matching)
we'd deadlock trying to acquire an inp lock we've already got.

Pass the inp pointer along with pf_route()/pf_route6().

PR: 228782
MFC after: 1 week