library/Native_Functions: add f_inet6_ntoa()

We have f_inet_ntoa() for converting IPv4 addresses to strings,
but so far there was no similar function for IPv6 addresses.

Change-Id: I0858cf8cb44a6673e19f3496c362d68fcdd7b18d
diff --git a/library/Native_Functions.ttcn b/library/Native_Functions.ttcn
index c43004a..c9cc948 100644
--- a/library/Native_Functions.ttcn
+++ b/library/Native_Functions.ttcn
@@ -11,6 +11,8 @@
 	external function f_inet_ntoa(in octetstring oct) return charstring;
 	/* like inet_ntoa() but input is host byte order */
 	external function f_inet_hntoa(in octetstring oct) return charstring;
+	/* direct import of inet_ntop(AF_INET6) C function, input net byte order */
+	external function f_inet6_ntoa(in octetstring oct) return charstring;
 
 	/* convert content of charstring to lower-case using tolower(3) */
 	external function f_str_tolower(in charstring input) return charstring;