MINOR: check: use auto SNI for QUIC checks

MINOR: check: use auto SNI for QUIC checks

By default, check SNI is set to the Host header when an HTTPS check is
performed. This patch extends this mode so that it is also active when
QUIC checks are executed.

This patch should improve reuse rate with checks. Indeed, SNI is also
already automatically set for normal traffic. The same value must be
used during check so that a connection hash match can be found.