Fixed Wireshark extcap command line parameter interface to mstpcap utility on Windows (Thank you Roland!).

Tested with Wireshark 1.99.7 on Windows.
To use extcap, run Wireshark and go to the About-dialog.  Find a tab located there named "Folders". Locate the extcap search path. Copy the mstpcap.exe to that folder, which may not exist.
Restart Wireshark, and look for "BACnet MS/TP on COMx" interfaces.
Configure the interface to change baud rate.
Start or stop the capture directly from the interface.

bacnet-stack/demo/mstpcap/main.c

@@ -433,47 +433,35 @@ uint16_t MSTP_Get_Reply(
 static char Capture_Filename[32] = "mstp_20090123091200.cap";
 static FILE *pFile = NULL;      /* stream pointer */
 #if defined(_WIN32)
-static HANDLE hPipe = NULL;     /* pipe handle */
-static PSECURITY_DESCRIPTOR pPipeSD = NULL;
+static HANDLE hPipe = INVALID_HANDLE_VALUE;     /* pipe handle */
 static void named_pipe_create(
-    char *name)
+    char *pipe_name)
 {
-    SECURITY_ATTRIBUTES sa;
-
-    pPipeSD = (PSECURITY_DESCRIPTOR)(malloc(SECURITY_DESCRIPTOR_MIN_LENGTH));
-    if (!pPipeSD) {
-        Exit_Requested = true;
-        return;
-    }
-    if (!InitializeSecurityDescriptor(pPipeSD, SECURITY_DESCRIPTOR_REVISION)) {
-        free(pPipeSD);
-        pPipeSD = NULL;
-        Exit_Requested = true;
-        return;
-    }
-    /* When an object has no DACL (when the pDacl parameter is NULL),
-       no protection is assigned to the object, and all access requests
-       are granted. To help maintain security, restrict access by using
-       a DACL. */
-    if (!SetSecurityDescriptorDacl(pPipeSD, TRUE, (PACL)NULL, FALSE)) {
-        free(pPipeSD);
-        pPipeSD = NULL;
-        Exit_Requested = true;
-        return;
-    }
-    // now set up the security attributes
-    sa.nLength = sizeof(SECURITY_ATTRIBUTES);
-    sa.lpSecurityDescriptor = pPipeSD;
-    sa.bInheritHandle = TRUE;
-    fprintf(stdout, "mstpcap: Creating Named Pipe \"%s\"\n", name);
-    hPipe =
-        CreateNamedPipe(name, PIPE_ACCESS_OUTBOUND,
-        PIPE_TYPE_MESSAGE | PIPE_WAIT,
-        PIPE_UNLIMITED_INSTANCES, 65536, 65536, 0L, &sa);
-    if (hPipe == INVALID_HANDLE_VALUE) {
-        RS485_Print_Error();
-        Exit_Requested = true;
-        return;
+    fprintf(stdout, "mstpcap: Creating Named Pipe \"%s\"\n", pipe_name);
+    /* create the pipe */
+    while (hPipe == INVALID_HANDLE_VALUE)
+    {
+        /* use CreateFile rather than CreateNamedPipe */
+        hPipe = CreateFile(
+            pipe_name,
+            GENERIC_READ |
+            GENERIC_WRITE,
+            0,
+            NULL,
+            OPEN_EXISTING,
+            0,
+            NULL);
+        if (hPipe != INVALID_HANDLE_VALUE) {
+            break;
+        }
+        /* if an error occured at handle creation */
+        if (!WaitNamedPipe(pipe_name, 20000)) {
+            printf("Could not open pipe: waited for 20sec!\n"
+                "If this message was issued before the 20sec finished,\n"
+                "then the pipe doesn't exist!\n");
+            Exit_Requested = true;
+            return;
+        }
     }
     ConnectNamedPipe(hPipe, NULL);
 }
@@ -864,13 +852,11 @@ static BOOL WINAPI CtrlCHandler(
 {
     dwCtrlType = dwCtrlType;
 
-    if (hPipe) {
+    if (hPipe != INVALID_HANDLE_VALUE) {
         FlushFileBuffers(hPipe);
         DisconnectNamedPipe(hPipe);
         CloseHandle(hPipe);
-    }
-    if (pPipeSD) {
-        free(pPipeSD);
+        hPipe = INVALID_HANDLE_VALUE;
     }
     /* signal to main loop to exit */
     Exit_Requested = true;