tests/pkd: input test payload buffer

Move the pkd test payload buffer into the arguments struct, to make
way for parameterizing the payload using command-line options.

Signed-off-by: Jon Simons <jon@jonsimons.org>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

tests/pkd/pkd_daemon.h

@@ -23,6 +23,11 @@ struct pkd_daemon_args {
     enum pkd_hostkey_type_e type;
     const char *hostkeypath;
 
+    struct {
+        const uint8_t *buf;
+        size_t len;
+    } payload;
+
     struct {
         int list;