BUG/MINOR: quic: Leak in qc_release_lost_pkts() for non in flight TX packets

BUG/MINOR: quic: Leak in qc_release_lost_pkts() for non in flight TX packets

Packets with null "in flight" lengths are kept as the others packets as sent
but not already acknowledeged in the by packet number space trees.
But qc_release_lost_pkts() relied on this in fligh length to release the
memory allocated for this packets. We must release the memory allocated for
all the lost packets regardless of their in fligh lengths.

Modify this function to do nothing if the list of lost packets passed
as argument is empty. Stop using <lost_bytes> variable to decide if some packets
memory must be released or not.
Modify the callers to stop checking if this list is empty.

Should helping in fixing memory leak as reported by Tristan in GH #1801.

Must be backported to 2.6.