MEDIUM: quic: implement a retransmit limit per frame

MEDIUM: quic: implement a retransmit limit per frame

Add a <loss_count> new field in quic_frame structure. This field is set
to 0 and incremented each time a sent packet is declared lost. If
<loss_count> reached a hard-coded limit, the connection is deemed as
failing and is closed immediately with a CONNECTION_CLOSE using
INTERNAL_ERROR.

By default, limit is set to 10. This should ensure that overall memory
usage is limited if a peer behaves incorrectly.

This should be backported up to 2.7.