BUG/MINOR: http-client: Reject any 101-switching-protocols response
Protocol updages are not supported by the http-client. So report an error is
a 101-switching-protocols response is received. Of course, it is unexpected
because the API is not designed to support upgrades. But it is better to
properly handle this case.
This patch could be backported as far as 2.6. It depends on the commit
"BUG/MINOR: http-client: Ignore 1XX interim responses in non-HTX mode".