Add a couple of debug logs

From patch by Thomas Shaddack <shaddack@shaddack.mauriceward.com>
https://www.improwis.com/projects/sw_SerialOverIP_RFC2217/

src/ttynvt.c

@@ -622,6 +622,7 @@ ttynvt_write(fuse_req_t req, const char *data, size_t size, off_t off,
     }
     else if (res != (int)size)
     {
+        DBG("%s: caution: tty->pollout set to 0\n", __func__);
         tty->pollout = 0;
     }
 
@@ -983,6 +984,7 @@ ttynvt_ioctl(fuse_req_t req, int cmd, void *arg,
             fuse_reply_ioctl(req, 0, &val, sizeof(int));
         break;
     default:
+        DBG("ERROR: Unsupported IOCTL\n");
         fuse_reply_err(req, ENOSYS);
         break;