BUILD: httpclient: include missing ssl_sock-t

It's needed for SSL_SOCK_VERIFY_NONE.
diff --git a/src/http_client.c b/src/http_client.c
index d0a1005..674c919 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -27,6 +27,7 @@
 #include <haproxy/log.h>
 #include <haproxy/proxy.h>
 #include <haproxy/server.h>
+#include <haproxy/ssl_sock-t.h>
 #include <haproxy/stream_interface.h>
 #include <haproxy/tools.h>