REGTESTS: quic: check Retry source address on a wildcard listener

REGTESTS: quic: check Retry source address on a wildcard listener

Add a new QUIC regtest for Retry emission through a listener bound on a
wildcard address. The Retry must be emitted with the address targeted
by the client as source, else a client relying on a connected socket
drops it and the handshake never completes.

This test relies on two haproxy instances, as QUIC client and server.
The QUIC server is reached through 127.0.0.2, while the kernel would
select 127.0.0.1 as source to reply to the client. As 127.0.0.2 is a
local address by default only on Linux, the BSD, macOS, Solaris and
generic targets are excluded. The wildcard listener port reuses the
number of the TCP port allocated by vtest for the same frontend, and the
CLI is used to wait for the QUIC listener to be ready before starting
the client.

This test is related to github issue #3503. As it requires QUIC backend
support, it may only be backported to 3.3 and above, along with the fix
"BUG/MEDIUM: quic: use datagram destination as source for Retry".