ccccinelle: add formatted comment for flag test
coccinelle: add script to generate flags test

This patch adds a script which can be used to generate a test
on coherence of flag usage.

By adding comment in the code, it is possible to declare that we
link a flag in a structure to a specific family of constant:

For example:
	/* coccinelle: Packet:flowflags:FLOW_PKT_ */
will trigger the generation on a test which verifies that the
flowflags field in Packet structure is only used with constant
starting by FLOW_PKT_.
coccinelle: dynamic testing through make check

This patch modify build system to have make to create the
struct-flags.cocci file by running struct-flags.py.

This way 'make check' is running the test defined from source
code.
detect-engine: do a direct update of flag

There is no reason not to update the flag directly. So do it
to avoid to crash the test.