add test for known vendor and unknown attribute

src/tests/unit/protocols/radius/vendor.txt

@@ -153,5 +153,15 @@ match f1 0b 1a 00 00 19 7f 26 ab cd ef
 decode-pair -
 match Extended-Attribute-1 = { Extended-Vendor-Specific-1 = { Nokia-SR = { raw.38 = 0xabcdef } } }
 
+#
+#  Known vendor, unknown attribute.  Microsoft will never add more RADIUS attributes to
+#  their dictionary, so we use that here.
+#
+encode-pair Vendor-Specific = { Microsoft = { raw.200 = 0xabcdef } }
+match 1a 0b 00 00 01 37 c8 05 ab cd ef
+
+decode-pair -
+match  Vendor-Specific = { Microsoft = { raw.200 = 0xabcdef } }
+
 count
-match 74
+match 78