[REQUEST] make "iface" available as variable for in checkip-command substitution

[SB211]

Updating IPv4 and IPv6 via different APIs of the DDNS provider for different interfaces used on the router (in my case: tun0 for the IPv6 and another NIC for IPv6 (delegated prefix) using the custom schema in inadyn.conf is source of some trouble. It would be very convenient if the config tag, i.e. "iface = igb0" could be available as a variable in "checkip-command = ", for instance, "%iface" or something like that, as it is provided for the substitutions for API, like %i the IP address.

Example:

custom dynv6_ip4 {
iface = tun0
username = blabla
ddns-server = ddns.server
ssl = true
hostname = { foe.bar.org, flue.bar.org, trumpet.foe.org }
checkip-command = ""ifconfig %iface inet |grep ...."
}

custom dynv6_ip6 {
iface = igb7
username = blabla
ddns-server = ddns.server
ssl = true
hostname = { foe.bar.org, flue.bar.org, trumpet.foe.org }
checkip-command = ""ifconfig %iface inet6 |grep ...."
}

[troglobit]

Like in any other Open Source project, your patch is welcome.