BUG/MINOR: quic: fix trace crash on datagram receive

BUG/MINOR: quic: fix trace crash on datagram receive

Recently, datagram reception architecture has been completely reworked
to improve performance. A regression has been introduced when using
traces in qc_rcv_buf() : datagram argument is uninitialized after recv
syscall. This may cause a crash as CIDs buffer is dereferenced.

Fix this by removing dgram argument from the affected trace. A new trace
is added after quic_dgram_init() to keep the ability to display the
received content.

This issue has caused failure of all QUIC interop testing.

No need to backport.