dnp3: set byte order when logging dnp3 src and dst

DNP3 uses little endian on the wire, for the most part this
is handled as the messages are deserialize. However, the link
header is a cast over raw data, so swap these bytes as they
are being logged.

Redmine issue:
https://redmine.openinfosecfoundation.org/issues/4173

src/output-json-dnp3.c

@@ -152,8 +152,8 @@ void JsonDNP3LogRequest(JsonBuilder *js, DNP3Transaction *dnp3tx)
     JsonDNP3LogLinkControl(js, dnp3tx->request_lh.control);
     jb_close(js);
 
-    jb_set_uint(js, "src", dnp3tx->request_lh.src);
+    jb_set_uint(js, "src", DNP3_SWAP16(dnp3tx->request_lh.src));
-    jb_set_uint(js, "dst", dnp3tx->request_lh.dst);
+    jb_set_uint(js, "dst", DNP3_SWAP16(dnp3tx->request_lh.dst));
 
     jb_open_object(js, "application");
 
@@ -186,8 +186,8 @@ void JsonDNP3LogResponse(JsonBuilder *js, DNP3Transaction *dnp3tx)
     JsonDNP3LogLinkControl(js, dnp3tx->response_lh.control);
     jb_close(js);
 
-    jb_set_uint(js, "src", dnp3tx->response_lh.src);
+    jb_set_uint(js, "src", DNP3_SWAP16(dnp3tx->response_lh.src));
-    jb_set_uint(js, "dst", dnp3tx->response_lh.dst);
+    jb_set_uint(js, "dst", DNP3_SWAP16(dnp3tx->response_lh.dst));
 
     jb_open_object(js, "application");