move the http_gzip_support check to the right place
move the http_gzip_support check to the right place

Ref: #2610

Thank you to @fgsch for spotting

Apologies to everyone for my insufficient understanding of the agreement
about which fixes we push during the soak in period after release.

gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache