BUG/MUNOR: http-ana: Use an unsigned integer for http_msg flags

BUG/MUNOR: http-ana: Use an unsigned integer for http_msg flags

In the commit 2954bcc1e (BUG/MINOR: http-ana: Don't switch message to DATA
when waiting for payload), the HTTP message flags were extended and don't
fit anymore in an unsigned char. So, we must use an unsigned integer now. It
is not a big deal because there was already a 6-bytes hole in the structure,
just after the flags. Now, there are a 3-bytes hold before.

This patch should fix the issue #2105. It is 2.8-specific, no backport
needed.