packet_cb: Add misssing include for ntohl().

Signed-off-by: Andreas Schneider <asn@cryptomilk.org>

src/packet_cb.c

@@ -24,6 +24,7 @@
 #include "config.h"
 
 #include <stdlib.h>
+#include <arpa/inet.h>
 
 #include "libssh/priv.h"
 #include "libssh/buffer.h"