typo fix: UNKOWN -> UNKNOWN

Change-Id: I008a4d7ad7160d1f07e7ceef712a5318a9368308
Signed-off-by: Andrey "Zed" Zaikin <zed.0xff@gmail.com>
diff --git a/src/vnet/mpls/mpls.c b/src/vnet/mpls/mpls.c
index be72d3f..aaaba39 100644
--- a/src/vnet/mpls/mpls.c
+++ b/src/vnet/mpls/mpls.c
@@ -274,7 +274,7 @@
 	;
       else
       {
-          error = clib_error_return (0, "unkown input: %U",
+          error = clib_error_return (0, "unknown input: %U",
                                      format_unformat_error, line_input);
           goto done;
       }