Remove `struct ndpi_packet_struct` from `struct ndpi_flow_struct` (#1319)

There are no real reasons to embed `struct ndpi_packet_struct` (i.e. "packet")
in `struct ndpi_flow_struct` (i.e. "flow"). In other words, we can avoid
saving dissection information of "current packet" into the "flow" state,
i.e. in the flow management table.

The nDPI detection module processes only one packet at the time, so it is
safe to save packet dissection information in `struct ndpi_detection_module_struct`,
reusing always the same "packet" instance and saving a huge amount of memory.
Bottom line: we need only one copy of "packet" (for detection module),
not one for each "flow".

It is not clear how/why "packet" ended up in "flow" in the first place.
It has been there since the beginning of the GIT history, but in the original
OpenDPI code `struct ipoque_packet_struct` was embedded in
`struct ipoque_detection_module_struct`, i.e. there was the same exact
situation this commit wants to achieve.

Most of the changes in this PR are some boilerplate to update something
like "flow->packet" into something like "module->packet" throughout the code.
Some attention has been paid to update `ndpi_init_packet()` since we need
to reset some "packet" fields before starting to process another packet.

There has been one important change, though, in ndpi_detection_giveup().
Nothing changed for the applications/users, but this function can't access
"packet" anymore.
The reason is that this function can be called "asynchronously" with respect
to the data processing, i.e in context where there is no valid notion of
"current packet"; for example ndpiReader calls it after having processed all
the traffic, iterating the entire session table.

Mining LRU stuff seems a bit odd (even before this patch): probably we need
to rethink it, as a follow-up.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/lib/protocols/rtp.c b/src/lib/protocols/rtp.c
index 111c57737..24f92afe2 100644
--- a/src/lib/protocols/rtp.c
+++ b/src/lib/protocols/rtp.c
@@ -77,7 +77,7 @@ static void ndpi_rtp_search(struct ndpi_detection_module_struct *ndpi_struct,
 			    struct ndpi_flow_struct *flow,
 			    const u_int8_t * payload, const u_int16_t payload_len) {
   u_int8_t payloadType, payload_type;
-  u_int16_t d_port = ntohs(flow->packet.udp->dest);
+  u_int16_t d_port = ntohs(ndpi_struct->packet.udp->dest);
   
   NDPI_LOG_DBG(ndpi_struct, "search RTP\n");
 
@@ -122,7 +122,7 @@ static void ndpi_rtp_search(struct ndpi_detection_module_struct *ndpi_struct,
 
 void ndpi_search_rtp(struct ndpi_detection_module_struct *ndpi_struct, struct ndpi_flow_struct *flow)
 {
-  struct ndpi_packet_struct *packet = &flow->packet;
+  struct ndpi_packet_struct *packet = &ndpi_struct->packet;
   u_int16_t source = ntohs(packet->udp->source);
   u_int16_t dest = ntohs(packet->udp->dest);