MINOR: server: Add "no-tfo" option.

Simple patch to add "no-tfo" option to "default-server" and "server" lines
to disable any usage of TCP fast open.

Must be backported to 2.0.
diff --git a/doc/configuration.txt b/doc/configuration.txt
index de092dc..2dbbb46 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -12127,6 +12127,13 @@
   It may also be used as "default-server" setting to reset any previous
   "default-server" "verifyhost" setting.
 
+no-tfo
+  This option may be used as "server" setting to reset any "tfo"
+  setting which would have been inherited from "default-server" directive as
+  default value.
+  It may also be used as "default-server" setting to reset any previous
+  "default-server" "tfo" setting.
+
 non-stick
   Never add connections allocated to this sever to a stick-table.
   This may be used in conjunction with backup to ensure that
@@ -12482,7 +12489,7 @@
   See the "tfo" bind option for more information about TCP fast open.
   Please note that when using tfo, you should also use the "conn-failure",
   "empty-response" and "response-timeout" keywords for "retry-on", or haproxy
-  won't be able to retry the connection on failure.
+  won't be able to retry the connection on failure. See also "no-tfo".
 
 track [<proxy>/]<server>
   This option enables ability to set the current state of the server by tracking
diff --git a/src/server.c b/src/server.c
index 15c8ffe..02fa2a4 100644
--- a/src/server.c
+++ b/src/server.c
@@ -583,6 +583,14 @@
 	return srv_disable_pp_flags(newsrv, SRV_PP_V2);
 }
 
+/* Parse the "no-tfo" server keyword */
+static int srv_parse_no_tfo(char **args, int *cur_arg,
+                            struct proxy *curproxy, struct server *newsrv, char **err)
+{
+	newsrv->flags &= ~SRV_F_FASTOPEN;
+	return 0;
+}
+
 /* Parse the "non-stick" server keyword */
 static int srv_parse_non_stick(char **args, int *cur_arg,
                                struct proxy *curproxy, struct server *newsrv, char **err)
@@ -1354,6 +1362,7 @@
 	{ "no-check-send-proxy", srv_parse_no_check_send_proxy, 0,  1 }, /* disable PROXY protol for health checks */
 	{ "no-send-proxy",       srv_parse_no_send_proxy,       0,  1 }, /* Disable use of PROXY V1 protocol */
 	{ "no-send-proxy-v2",    srv_parse_no_send_proxy_v2,    0,  1 }, /* Disable use of PROXY V2 protocol */
+	{ "no-tfo",              srv_parse_no_tfo,              0,  1 }, /* Disable use of TCP Fast Open */
 	{ "non-stick",           srv_parse_non_stick,           0,  1 }, /* Disable stick-table persistence */
 	{ "observe",             srv_parse_observe,             1,  1 }, /* Enables health adjusting based on observing communication with the server */
 	{ "pool-max-conn",       srv_parse_pool_max_conn,       1,  1 }, /* Set the max number of orphan idle connections, 0 means unlimited */