BUG/MINOR: http-act: Use the good message to test strict rewritting mode

BUG/MINOR: http-act: Use the good message to test strict rewritting mode

Since the strict rewritting mode was introduced, actions manipulating headers
(set/add/replace) always rely on the request message to test if the
HTTP_MSGF_SOFT_RW flag is set or not. But, of course, we must only rely on the
request for http-request rules. For http-response rules, we must use the
response message.

This patch must be backported if the strict rewritting is backported too.