Check file handle limit on startup (RIPD-442, RIPD-1024):

Calculate the number of file descriptors that are needed during
execution based on the configuration file, with a hard floor
of 1024, adjusting the limit if possible. Refuse to run if enough
fds are not available.

Additionally, allow administrators to limit the number of incoming
connections a configured port will accept. By default no limit is
imposed.

src/ripple/overlay/impl/OverlayImpl.cpp

@@ -775,6 +775,12 @@ OverlayImpl::size()
     return ids_.size ();
 }
 
+int
+OverlayImpl::limit()
+{
+    return m_peerFinder->config().maxPeers;
+}
+
 Json::Value
 OverlayImpl::crawl()
 {