pptpd: Add uci configuration for PPTPD.

Signed-off-by: Bruno Randolf <br1@einfach.org>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@38445 3c298f89-4303-0410-b956-a3cf2f4a3e73
isc-dhcp: dhcrelay: Add more UCI options

Add more options to dhcrelay UCI and init script:

- enabled
- interfaces: Listen interfaces
- relay_mode: What to do about packets that already have a relay option

Also mark /etc/config/dhcrelay as conffile

Signed-off-by: Bruno Randolf <br1@einfach.org>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@38446 3c298f89-4303-0410-b956-a3cf2f4a3e73
isc-dhcp: dhcrelay: Add RFC3527 link selection sub-option

RFC3527 link selection sub-option is used to select the "uplink" interface of
dhcrelay in cases where the DHCP server does not know how to reach the dhcrelay
based on the DHCP range. This can happen in weird network configurations like
Mesh networks.

Signed-off-by: Bruno Randolf <br1@einfach.org>

git-svn-id: svn://svn.openwrt.org/openwrt/packages@38447 3c298f89-4303-0410-b956-a3cf2f4a3e73