snap: cache early dtls packets in race condition

If SCTP is negotiated after the DTLS handshake has been completed there exists a race condition with SNAP wherein the answerer can start opening  channels (and send data) before the answer with the sctp-init arrives at the offerer.

Cache a limited amount of decrypted and authenticated packets and replay them after receiving the answer. This problem also exists for non-snap but is mitigated by the symmetric open on both sides so the loss in one direction does not matter much.

Note: doing a "half-open" on the offerer socket does not work as it can not send acknowledgements of received packets due to the missing peer verification tag.

Bug: webrtc:426480601
Change-Id: Ic8ee193b6ca8774943e19e37073814af144ce7d4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/478160
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Reviewed-by: Victor Boivie <boivie@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48041}