BUG/MINOR: tcpcheck: Set socks4 and send-proxy flags before the connect call

Since the health-check refactoring in the 2.2, the checks through a socks4 proxy
are broken. To fix this bug, CO_FL_SOCKS4 flag must be set on the connection
before calling the connect() callback function because this flags is checked to
use the right destination address. The same is done for the CO_FL_SEND_PROXY
flag for a consistency purpose.

A reg-test has been added to test the "check-via-socks4" directive.

This patch must be backported to 2.2.
diff --git a/reg-tests/checks/tcp-checks-socks4.vtc b/reg-tests/checks/tcp-checks-socks4.vtc
new file mode 100644
index 0000000..bd0d3db
--- /dev/null
+++ b/reg-tests/checks/tcp-checks-socks4.vtc
@@ -0,0 +1,63 @@
+varnishtest "Health-checks: basic HTTP health-check though a socks4 proxy"
+#REQUIRE_VERSION=2.0
+#REGTEST_TYPE=slow
+feature ignore_unknown_macro
+
+# This scripts tests a simple HTTP health-checks though a socks4 proxy.
+
+server s1 {
+} -start
+
+server socks {
+  ## get socks4 request
+  recv 16
+
+  ## send socks4 response :
+  ##   constant(1): 0x00
+  ##   statut(1)  : 0x5a (success)
+  ##   padding(6) : ignored
+  sendhex "005A000000000000"
+
+  rxreq
+  expect req.method == OPTIONS
+  expect req.url == /
+  expect req.proto == HTTP/1.0
+  txresp
+} -start
+
+syslog S1 -level notice {
+    recv
+    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Proxy be1 started."
+    recv
+    expect ~ "[^:\\[ ]\\[${h1_pid}\\]: Health check for server be1/srv succeeded, reason: Layer7 check passed.+code: 200.+check duration: [[:digit:]]+ms, status: 1/1 UP."
+} -start
+
+haproxy h1 -conf {
+    defaults
+        mode tcp
+        timeout client 1s
+        timeout server 1s
+        timeout connect 100ms
+
+    backend be1
+        log ${S1_addr}:${S1_port} daemon
+        option log-health-checks
+        option httpchk
+        server srv ${s1_addr}:${s1_port} socks4 ${h1_socks_addr}:${h1_socks_port} check-via-socks4 check inter 1s rise 1 fall 1
+
+    listen socks
+        bind "fd@${socks}"
+        tcp-request inspect-delay 500ms
+        ## Accept socks4 request on 16 bytes :
+        ##    version(1) : 0x04
+        ##    command(1) : 0x01
+        ##    port(2)    : ${s1_port}
+        ##    addr(4)    : ${s1_addr}
+        ##    user-id    : "HAProxy\0"
+        tcp-request content accept if { req.len eq 16 } { req.payload(0,1) -m bin "04" } { req.payload(1,1) -m bin "01" } { req.payload(2,2),hex,hex2i eq ${s1_port} } { req.payload(4,4),hex,hex2i -m ip ${s1_addr} } { req.payload(8,8) -m bin "484150726F787900" }
+        tcp-request content reject
+        server srv ${socks_addr}:${socks_port}
+
+} -start
+
+syslog S1 -wait
diff --git a/src/tcpcheck.c b/src/tcpcheck.c
index 5bd237a..b9ef380 100644
--- a/src/tcpcheck.c
+++ b/src/tcpcheck.c
@@ -1073,6 +1073,24 @@
 	conn_prepare(conn, proto, xprt);
 	cs_attach(cs, check, &check_conn_cb);
 
+	if ((connect->options & TCPCHK_OPT_SOCKS4) && s && (s->flags & SRV_F_SOCKS4_PROXY)) {
+		conn->send_proxy_ofs = 1;
+		conn->flags |= CO_FL_SOCKS4;
+	}
+	else if ((connect->options & TCPCHK_OPT_DEFAULT_CONNECT) && s && s->check.via_socks4 && (s->flags & SRV_F_SOCKS4_PROXY)) {
+		conn->send_proxy_ofs = 1;
+		conn->flags |= CO_FL_SOCKS4;
+	}
+
+	if (connect->options & TCPCHK_OPT_SEND_PROXY) {
+		conn->send_proxy_ofs = 1;
+		conn->flags |= CO_FL_SEND_PROXY;
+	}
+	else if ((connect->options & TCPCHK_OPT_DEFAULT_CONNECT) && s && s->check.send_proxy && !(check->state & CHK_ST_AGENT)) {
+		conn->send_proxy_ofs = 1;
+		conn->flags |= CO_FL_SEND_PROXY;
+	}
+
 	status = SF_ERR_INTERNAL;
 	next = get_next_tcpcheck_rule(check->tcpcheck_rules, rule);
 	if (proto && proto->connect) {
@@ -1102,23 +1120,6 @@
 	else if ((connect->options & TCPCHK_OPT_DEFAULT_CONNECT) && s && s->check.alpn_str)
 		ssl_sock_set_alpn(conn, (unsigned char *)s->check.alpn_str, s->check.alpn_len);
 #endif
-	if ((connect->options & TCPCHK_OPT_SOCKS4) && s && (s->flags & SRV_F_SOCKS4_PROXY)) {
-		conn->send_proxy_ofs = 1;
-		conn->flags |= CO_FL_SOCKS4;
-	}
-	else if ((connect->options & TCPCHK_OPT_DEFAULT_CONNECT) && s && s->check.via_socks4 && (s->flags & SRV_F_SOCKS4_PROXY)) {
-		conn->send_proxy_ofs = 1;
-		conn->flags |= CO_FL_SOCKS4;
-	}
-
-	if (connect->options & TCPCHK_OPT_SEND_PROXY) {
-		conn->send_proxy_ofs = 1;
-		conn->flags |= CO_FL_SEND_PROXY;
-	}
-	else if ((connect->options & TCPCHK_OPT_DEFAULT_CONNECT) && s && s->check.send_proxy && !(check->state & CHK_ST_AGENT)) {
-		conn->send_proxy_ofs = 1;
-		conn->flags |= CO_FL_SEND_PROXY;
-	}
 
 	if (conn_ctrl_ready(conn) && (connect->options & TCPCHK_OPT_LINGER)) {
 		/* Some servers don't like reset on close */