xl2tpd: fix invoking xl2tpd-control

Upstream commit 90884c62 ("xl2tpd-control refactoring") introduced in
1.3.16 changed command names

The l2tp protocol handler part was from @danvd in pull request
openwrt/packages#13866

Fixes f07319d6 ("xl2tpd: bump to version 1.3.16")

Ref: https://github.com/openwrt/packages/pull/13866
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

net/xl2tpd/patches/0002-xl2tpd-control-fix-typo-in-usage.patch

@@ -0,0 +1,22 @@
+From 06bd6af97055071be5ed0f83a808032688a503db Mon Sep 17 00:00:00 2001
+From: Yousong Zhou <yszhou4tech@gmail.com>
+Date: Thu, 12 Nov 2020 14:33:05 +0800
+Subject: [PATCH] xl2tpd-control: fix typo in usage
+
+---
+ xl2tpd-control.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/xl2tpd-control.c b/xl2tpd-control.c
+index d1df0f6..2e683c8 100644
+--- a/xl2tpd-control.c
++++ b/xl2tpd-control.c
+@@ -96,7 +96,7 @@ void usage()
+             "   --help  show this help message\n\n"
+             "List of supported commands:\n"
+             "add-lac, status-lac, remove-lac, connect-lac, disconnect-lac\n"
+-            "add-lns, status-lns, remove-lns, avaliable\n\n"
++            "add-lns, status-lns, remove-lns, available\n\n"
+             "See xl2tpd-control(8) man page for more details.\n");
+ }
+