vnstat: import from packages, add myself as maintainer

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

net/vnstat/files/vnstat.defaults

@@ -0,0 +1,13 @@
+#!/bin/sh
+
+wan="$(uci -P/var/state get network.wan.ifname)"
+
+if [ -n "$wan" ]; then
+	uci -q batch <<-EOF >/dev/null
+		del_list vnstat.@vnstat[-1].interface=$wan
+		add_list vnstat.@vnstat[-1].interface=$wan
+		commit vnstat
+	EOF
+fi
+
+exit 0