Extend ttl_seen valid lifetime of an attestation/aggregate to 2 epochs

[philknows]

Problem description

We've also confirmed that we are seeing spam post-Deneb under the aggregate channel.

Solution description

Then net effect of the above change is that peers are allowed to republish old aggregates and attestations and libp2p will not stop the spread with the settings we recommend - instead the messages will have to be stopped with the "attestation cover rule" or similar, even though they have been observed already.

Additional context

Reference: ethereum/consensus-specs#3627