Ensure that only the rxthread gets to use h2->cond in h2_send_get
Ensure that only the rxthread gets to use h2->cond in h2_send_get

Future-proofing to avoid mistakenly introducing another race down the
line.

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