Fixes to DATAGRAM, BBR, handshake and memory leak
- Generate ACK for DATAGRAM frame while avoid RETX (issue #312 #325).
- Fix BBR end of startup phase detection (issue #328).
- Fix HTTP/3 v1 retry handling (issue #332)
- Fix memory leak when reset dcid (issue #333)
- Fix double decrement for ifc_active_cids_count (#334)
- Fix uninitialized value in frame_reader/frame_writer (#316)
- Remove a few overly strict asserts.