DOC: quic: fix recommandation for bind on multiple address

DOC: quic: fix recommandation for bind on multiple address

Documentation falsely mentions that binding on multiple addresses is
forbidden for QUIC listeners. This is not the case. Moreover, this
behavior is reliable when using destination address retrieval on receive
via IP_PKTINFO, which allows to determine the proper source address for
response.

This should be backported up to 2.7. On 2.6 specific source address
definition on sendmsg via IP_PKTINFO is not implemented. As such, bind
on multiple addresses should remain forbidden for this release.