MINOR: quic: Add new traces about by connection RX buffer handling

MINOR: quic: Add new traces about by connection RX buffer handling

Move quic_rx_pkts_del() out of quic_conn.h to make it benefit from the TRACE API.
Add traces which already already helped in diagnosing an issue encountered with
ngtcp2 which sent too much 1RTT packets before the handshake completion. This
has been fixed here after having discussed with Tasuhiro on QUIC dev slack:

https://github.com/ngtcp2/ngtcp2/pull/663

Must be backported to 2.7.