rp-pppoe: Add back from oldpackages with build fixes and enhanced packaging

Add back from oldpackages with fixes for build errors and UCIfication
(for LuCI app submitted in a related PR (against LuCI repo)).

NOTE: Untested packages have been marked with @BROKEN.  This can
be undone of others report success with the sniffer

Signed-off-by: Daniel Dickinson <lede@daniel.thecshore.com>

net/rp-pppoe/files/pppoe.config

@@ -0,0 +1,23 @@
+#config pppoe_server
+#	option interface eth1
+#	option ac_name access-concentrator-name
+#	list service_name service-name1
+#	list service_name service-name2
+#	option maxsessionsperpeer 0
+#	option localip 192.168.2.1
+#	option firsremoteip 192.168.2.2
+#	option maxsessions 64
+#	option optionsfile /etc/ppp/pppoe-server-options
+#	option randomsessions 1
+#	option unit 0
+#	option offset 0
+#	option timeout 60
+#	option mss 1468
+#	option sync 0
+
+#config pppoe_relay
+#	list server_interface eth1
+#	list client_interface eth0
+#	list both_interface eth2
+#	option maxsessions 64
+#	option timeout 60