BUG/MINOR: quic: fix deprecated warning for window size keyword

BUG/MINOR: quic: fix deprecated warning for window size keyword

QUIC configuration was cleaned up in the previous release. Several
global keyword names were changed to unify the configuration. For each
of them the older keyword is marked as deprecated, with a warning to
mention the newer alternative.

This patch fixes the warning for 'tune.quic.frontend.default-max-size'
as the alternative proposed was not correct. The proper value now is
'tune.quic.fe.cc.max-win-size'.

This must be backported up to 3.3.