BUG/MINOR: lua: Fix return value of Socket.settimeout

The `socket.tcp.settimeout` method of Lua returns `1` in all cases,
while the `Socket.settimeout` method of haproxy returns `0` in all
cases. This breaks the `socket.http` module, because it validates
the return value of `settimeout`.

This bug was introduced in commit 7e7ac32dad1e15c19152d37aaf9ea6b3f00a7226
(which is the very first commit adding the Socket class to Lua). This
bugfix should be backported to every branch containing that commit:
- 1.6
- 1.7
- 1.8

A test case for this bug is as follows:

The 'Test' response header will contain an HTTP status code with the
patch applied and will be zero (nil) without the patch applied.

http.lua:
  http = require("socket.http")

  core.register_action("bug", { "http-req" }, function(txn)
  	local b, c, h = http.request {
  		url = "http://93.184.216.34",
  		headers = {
  			Host = "example.com"
  		},
  		create = core.tcp,
  		redirect = false
  	}

  	txn:set_var("txn.foo", c)
  end)

haproxy.cfg:
  global
  	lua-load /scratch/haproxy/http.lua

  frontend fe
  	bind 127.0.0.1:8080
  	http-request lua.bug
  	http-response set-header Test %[var(txn.foo)]

  	default_backend be

  backend be
  	server s example.com:80

src/hlua.c

@@ -2490,7 +2490,7 @@ __LJMP static int hlua_socket_settimeout(struct lua_State *L)
 	s->res.wto = tmout;
 	xref_unlock(&socket->xref, peer);
 
-	return 0;
+	return 1;
 }
 
 __LJMP static int hlua_socket_new(lua_State *L)