MINOR: ssl: Release Servers SSL context when HAProxy is shut down

[wt: could be backported to 1.5 as well]
diff --git a/include/proto/ssl_sock.h b/include/proto/ssl_sock.h
index 1b6c081..b877580 100644
--- a/include/proto/ssl_sock.h
+++ b/include/proto/ssl_sock.h
@@ -46,6 +46,7 @@
 int ssl_sock_prepare_ctx(struct bind_conf *bind_conf, SSL_CTX *ctx, struct proxy *proxy);
 int ssl_sock_prepare_all_ctx(struct bind_conf *bind_conf, struct proxy *px);
 int ssl_sock_prepare_srv_ctx(struct server *srv, struct proxy *px);
+void ssl_sock_free_srv_ctx(struct server *srv);
 void ssl_sock_free_all_ctx(struct bind_conf *bind_conf);
 int ssl_sock_load_ca(struct bind_conf *bind_conf, struct proxy *px);
 void ssl_sock_free_ca(struct bind_conf *bind_conf);