Fix bug in RFC 5447 dictionary.

Pick up the current version ("current" as in "picked up from a recent
checkout of the FreeRADIUS/freeradius-server repository on GitHub") of
dictionary.rfc5447.

See

    FreeRADIUS/freeradius-server#2269

and some of the discussion in

    the-tcpdump-group/tcpdump#636

Change-Id: Ib21838684ac250ff1f02fcea6c1e5ca865b4b6ff
Reviewed-on: https://code.wireshark.org/review/28935
Reviewed-by: Guy Harris <guy@alum.mit.edu>
(cherry picked from commit 7b6181a)
Reviewed-on: https://code.wireshark.org/review/28937

radius/dictionary.rfc5447

@@ -4,9 +4,13 @@
 #	Attributes and values defined in RFC 5447.
 #	http://www.ietf.org/rfc/rfc5447.txt
 #
-#	$Id: 2fb1d08eb283d19e7d641c3d997ea51e42bbee58 $
+#	$Id: 44021756d09926711aa40b207712055743312c69 $
 #
 
 # 64-bit bit field
 ATTRIBUTE	MIP6-Feature-Vector			124	octets
-ATTRIBUTE	MIP6-Home-Link-Prefix			125	ipv6prefix
+
+#
+#  Encoded as one octet prefix, followed by 16 octets of address information.
+#
+ATTRIBUTE	MIP6-Home-Link-Prefix			125	octets