stream-tcp: no checksum alert if validation is off

This patch disables checksum alert if checksum-validation is set
to no in the configuration file. Without this patch, when parsing
a pcap which checksum offloading, it was not possible to get rid
of event caused by checksum validation.

src/stream-tcp.c

@@ -3737,12 +3737,14 @@ TmEcode StreamTcp (ThreadVars *tv, Packet *p, void *data, PacketQueue *pq, Packe
         return TM_ECODE_OK;
     }
 
-    if ((stream_config.flags & STREAMTCP_INIT_FLAG_CHECKSUM_VALIDATION) &&
-            (StreamTcpValidateChecksum(p) == 0))
-    {
+    if (stream_config.flags & STREAMTCP_INIT_FLAG_CHECKSUM_VALIDATION) {
+        if (StreamTcpValidateChecksum(p) == 0) {
             SCPerfCounterIncr(stt->counter_tcp_invalid_checksum, tv->sc_perf_pca);
             return TM_ECODE_OK;
         }
+    } else {
+        p->flags |= PKT_IGNORE_CHECKSUM;
+    }
 
     PACKET_PROFILING_APP_RESET(&stt->ra_ctx->dp_ctx);