BUG/MINOR: quic: Possible RX packet memory leak under heavy load

BUG/MINOR: quic: Possible RX packet memory leak under heavy load

This bug could be reproduced with -dMfail and h2load generating plenty of connections.
A "show pools" CLI command showed that some memory in relation with RX packet pool
was never release. Furthermore, adding a RX packet counter to each connection
and a BUG_ON() in quic_conn_release() has proved that this unreleased memory
was in relation with RX packet which were not linked to a connection.

The responsible is quic_dgram_parse() which does not release some RX packet
memory before exiting after the connection thread affinity has changed.

Must be backported as far as 2.7.