pf: Don't pfsync states with unrecoverable routing information

States created by route-to rules can't be trusted when received with
pfsync version 1301 as they lack the rt and rt_kif information. They
are imported, though, and pf_route() function attempts to recover
the missing information for every forwarded packet.

Move the recovery operation to pfsync_state_import() so that it's
performed only once and if it's impossible don't import the state.
Add an additional check for cases when recovery might produce wrong
results.

Reviewed by: kp
Approved by: kp (mentor)
Sponsored by: InnoGames GmbH
Differential Revision: https://reviews.freebsd.org/D47906