lib/in46a: Introduce in46a_netmasklen API

Change-Id: I06e3e038afd8f7afaec2a3fa67b1616500c8db80
diff --git a/tests/lib/in46a_test.ok b/tests/lib/in46a_test.ok
index b115444..9a0ff7a 100644
--- a/tests/lib/in46a_test.ok
+++ b/tests/lib/in46a_test.ok
@@ -15,3 +15,5 @@
 in46a_within_mask(10.11.12.14, 10.11.12.12, 30) = 1
 testing in46a_to_eua()
 Testing in46a_from_eua()
+Testing in46a_netmasklen() with IPv4 addresses
+Testing in46a_netmasklen() with IPv6 addresses