REGTESTS: Fix h1_to_h2_upgrade.vtc to force h2 on first bind line

REGTESTS: Fix h1_to_h2_upgrade.vtc to force h2 on first bind line

With VTEST, It seems possible to receive the H2 preface in 2 packets. So the
preface cannot be matched and the H1 to H2 upgrade is not performed as
expected. The script was fixed by forcing the H2 proto on the first bind
line.

The problem with the preface matching will be reviewed later.