BUG/MINOR: quic: Ensure to be able to build datagrams to be retransmitted

When retransmitting datagrams with two coalesced packets inside, the second
packet was not taken into consideration when checking there is enough space
into the network for the datagram, especially when limited by the anti-amplification.

Must be backported to 2.6 and 2.7.
1 file changed