ppp: Allow PPTP over a specified interface

In a dual-WAN setup, it's useful to specify an interface over which to
have PPTP.

Signed-off-by: Daniel Gimpelevich <daniel@gimpelevich.san-francisco.ca.us>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44507 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/network/services/ppp/files/ppp.sh

@@ -181,6 +181,7 @@ proto_pppoa_teardown() {
 proto_pptp_init_config() {
 	ppp_generic_init_config
 	proto_config_add_string "server"
+	proto_config_add_string "interface"
 	available=1
 	no_device=1
 }
@@ -189,10 +190,11 @@ proto_pptp_setup() {
 	local config="$1"
 	local iface="$2"
 
-	local ip serv_addr server
-	json_get_var server server && {
+	local ip serv_addr server interface
+	json_get_vars interface server
+	[ -n "$server" ] && {
 		for ip in $(resolveip -t 5 "$server"); do
-			( proto_add_host_dependency "$config" "$ip" )
+			( proto_add_host_dependency "$config" "$ip" $interface )
 			serv_addr=1
 		done
 	}