partly support getting IPv6 addresses

- gets interface id from ppp
- runs odhcpc to get RA and prefix delegation
- doesn't do anything useful with the data yet

examples/udhcp6-script.fnl

@@ -0,0 +1,47 @@
+
+
+(fn write-value [name value]
+  (with-open [fout (io.open name :w)]
+    (when value (fout:write value))))
+
+(write-value "state" (. arg 2))
+(write-value "ifname" (. arg 1))
+
+(fn write-value-from-env [name]
+  (write-value name (os.getenv (string.upper name))))
+
+(let [wanted
+      [
+       :addresses
+       :aftr
+       :cer
+       :domains
+       :lw406
+       :mape
+       :mapt
+       :ntp_fqdn
+       :ntp_ip
+       :option_1
+       :option_2
+       :option_3
+       :option_4
+       :option_5
+       :passthru
+       :prefixes
+       :ra_addresses
+       :ra_dns
+       :ra_domains
+       :ra_hoplimit
+       :ra_mtu
+       :ra_reachable
+       :ra_retransmit
+       :ra_routes
+       :rdnss
+       :server
+       :sip_domain
+       :sip_ip
+       :sntp_ip
+       :sntp_fqdn
+       ]]
+  (each [_ n (ipairs wanted)]
+    (write-value-from-env n)))