MINOR: quic: Increase the QUIC connections RX buffer size (upto 64Kb)

With ~1500 bytes QUIC datagrams, we can handle less than 200 datagrams
which is less than the default maxpollevents value. This should reduce
the chances of fulfilling the connections RX buffers as reported by
Tristan in GH #1737.

Must be backported to 2.6.
1 file changed