library: Implement f_inet6_addr function

It can be used to parse IPv6 functions, since inet_addr supports IPv4
only.

Change-Id: Icb6dd38462501895d1b4409a3c530793917bd803
diff --git a/library/Native_Functions.ttcn b/library/Native_Functions.ttcn
index 31bc767..d59670a 100644
--- a/library/Native_Functions.ttcn
+++ b/library/Native_Functions.ttcn
@@ -1,5 +1,7 @@
 module Native_Functions {
 
+	/* direct import of inet_pton(AF_INET6) C function, returns net byte order */
+	external function f_inet6_addr(in charstring ch) return octetstring;
 	/* direct import of inet_addr() C function, returns net byte order */
 	external function f_inet_addr(in charstring ch) return octetstring;
 	/* like inet_addr() but return is host byte order */