* The number of packets sent or lost in ECN validation must be tracked per
  QUIC packets and packet number space.
* Handle coalesced QUIC packets correctly.

Fixes: https://github.com/ngtcp2/ngtcp2/issues/261

Fixes: https://github.com/ngtcp2/ngtcp2/issues/257

Without these changes, library was failing to build on both Windows and
FreeBSD.

Remove conn and user_data from ngtcp2_rand in order to use it before
conn is initialized.