Simplified a method.

src/dht.cpp

@@ -71,9 +71,7 @@ set_nonblocking(int fd, int nonblocking)
     if (rc < 0)
         return false;
     rc = fcntl(fd, F_SETFL, nonblocking?(rc | O_NONBLOCK):(rc & ~O_NONBLOCK));
-    if (rc < 0)
-        return false;
-    return true;
+    return !(rc < 0);
 }
 
 #endif