MINOR: http-act/tcp-act: Add "set-log-level" for tcp content rules

MINOR: http-act/tcp-act: Add "set-log-level" for tcp content rules

It is now possible to set the stream log level from a "tcp-request content"
or "tcp-response content" ruleset. To do so, the action parsing is moved in
stream.c and the action evaluation is handled in a dedicated function.

This patch should fix issue #1306. It may be backported as far as 2.2 if
necessary.