session server BUGFIX limit number of connect retries

... with a single socket.
Refs cesnet/netopeer2#823
diff --git a/src/session_server.c b/src/session_server.c
index 9c1698e..6ba051a 100644
--- a/src/session_server.c
+++ b/src/session_server.c
@@ -3075,8 +3075,15 @@
     struct timespec ts_cur;
     char *ip_host;
 
-    sock = nc_sock_connect(endpt->address, endpt->port, 5, &endpt->ka, &endpt->sock_pending, &ip_host);
+    sock = nc_sock_connect(endpt->address, endpt->port, NC_SOCKET_CH_TIMEOUT, &endpt->ka, &endpt->sock_pending, &ip_host);
     if (sock < 0) {
+        ++endpt->sock_retries;
+        if (endpt->sock_retries == NC_SOCKET_CH_RETRIES) {
+            ERR("Failed to connect socket %d after %d retries, closing.", endpt->sock_pending, NC_SOCKET_CH_RETRIES);
+            close(endpt->sock_pending);
+            endpt->sock_pending = -1;
+            endpt->sock_retries = 0;
+        }
         return NC_MSG_ERROR;
     }
     /* no need to store the socket as pending any longer */