CONTRIB: ip6range: add a network IPv6 range to mask converter

It can be used to convert some Maxmind geolocation IPv6 lists using the
CVS format to IPv6 networks format.
diff --git a/contrib/ip6range/Makefile b/contrib/ip6range/Makefile
new file mode 100644
index 0000000..55849b6
--- /dev/null
+++ b/contrib/ip6range/Makefile
@@ -0,0 +1,13 @@
+CC       = gcc
+OPTIMIZE = -O3
+LDFLAGS  = -s
+
+OBJS     = ip6range
+
+all: $(OBJS)
+
+%: %.c
+	$(CC) $(LDFLAGS) $(OPTIMIZE) -o $@ $^
+
+clean:
+	rm -f $(OBJS) *.o *.a *~