decode: introduce PacketCallocExtPkt function

In flow timeout handling we need a function that allocate and blank
a place that will be used to put constructed packet data. This new
function has no other goal.

src/decode.c

@@ -171,6 +171,18 @@ Packet *PacketGetFromQueueOrAlloc(void)
     return p;
 }
 
+inline int PacketCallocExtPkt(Packet *p, int datalen)
+{
+    if (! p->ext_pkt) {
+        p->ext_pkt = SCCalloc(1, datalen);
+        if (unlikely(p->ext_pkt == NULL)) {
+            SET_PKT_LEN(p, 0);
+            return -1;
+        }
+    }
+    return 0;
+}
+
 /**
  *  \brief Copy data to Packet payload at given offset
  *

src/decode.h

@@ -835,6 +835,7 @@ Packet *PacketGetFromAlloc(void);
 void PacketDecodeFinalize(ThreadVars *tv, DecodeThreadVars *dtv, Packet *p);
 void PacketFree(Packet *p);
 void PacketFreeOrRelease(Packet *p);
+int PacketCallocExtPkt(Packet *p, int datalen);
 int PacketCopyData(Packet *p, uint8_t *pktdata, int pktlen);
 int PacketSetData(Packet *p, uint8_t *pktdata, int pktlen);
 int PacketCopyDataOffset(Packet *p, int offset, uint8_t *data, int datalen);