Note that while PF_KEYv2 also uses sequence numbers to identify acquires,
which we currently don't use correctly by the way, it does not include
information about the packet that triggered an acquire. What we receive
in src and dst, and currently forward as traffic selectors, are actually
the designated endpoints of the SA. So especially in tunnel mode this is
useless to do narrowing on the responder (these addresses might not even
match the configured TS).