ikev2: fix string in api

Type: fix

key file name should be a string and not array of u8.

Change-Id: I7d280d2397030e73732b374ad9d3146fad0bb19f
Signed-off-by: Filip Tehlar <ftehlar@cisco.com>
diff --git a/src/plugins/ikev2/ikev2.api b/src/plugins/ikev2/ikev2.api
index 8c56c98..325e654 100644
--- a/src/plugins/ikev2/ikev2.api
+++ b/src/plugins/ikev2/ikev2.api
@@ -142,7 +142,7 @@
   u32 client_index;
   u32 context;
 
-  u8 key_file[256];
+  string key_file[256];
   option vat_help = "file <absolute_file_path>";
 };