QUIC: keep stream sockaddr and addr_text constant.

QUIC: keep stream sockaddr and addr_text constant.

HTTP and Stream variables $remote_addr and $binary_remote_addr rely on
constant client address, particularly because they are cacheable.
However, QUIC client may migrate to a new address.  While there's no perfect
way to handle this, the proposed solution is to copy client address to QUIC
stream at stream creation.

The change also fixes truncated $remote_addr if migration happened while the
stream was active.  The reason is addr_text string was copied to stream by
value.