Add missing #include's to sftpserver.h

Presumably this header is always imported with all the other necessary ones so
it doesn't usually make a difference, but generating Julia bindings from the
header by itself requires all the types to be defined (e.g. ssh_session,
ssh_channel, etc).

Signed-off-by: James Wrigley <james@puiterwijk.org>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
(cherry picked from commit 9ad2f6b3b1)

include/libssh/sftpserver.h

@@ -29,6 +29,10 @@ extern "C" {
 #endif
 
 #include <stdint.h>
+
+#include "libssh/libssh.h"
+#include "libssh/sftp.h"
+
 /**
  * @defgroup libssh_sftp_server The libssh SFTP server API
  *