priv.h: Fix “MAX_PACKAT_LEN” typo in #ifndef guard

The preprocessor guard was previously effectively inoperative;
it used to read “MAX_PACKAT_LEN” (note the ‘A’!), now is ‘E’.

Signed-off-by: Paul Capron <paul@fragara.com>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>

include/libssh/priv.h

@@ -167,7 +167,7 @@ int gettimeofday(struct timeval *__p, void *__t);
 #include "libssh/callbacks.h"
 
 /* some constants */
-#ifndef MAX_PACKAT_LEN
+#ifndef MAX_PACKET_LEN
 #define MAX_PACKET_LEN 262144
 #endif
 #ifndef ERROR_BUFFERLEN