packets: Fix ssh_send_keepalive()

ssh_send_keepalive() should use global_request() to properly configure
the state machine for packet filtering.

Signed-off-by: Nicolas Viennot <nicolas@viennot.biz>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/libssh/channels.h

@@ -98,5 +98,9 @@ int ssh_channel_flush(ssh_channel channel);
 uint32_t ssh_channel_new_id(ssh_session session);
 ssh_channel ssh_channel_from_local(ssh_session session, uint32_t id);
 void ssh_channel_do_free(ssh_channel channel);
+int ssh_global_request(ssh_session session,
+                       const char *request,
+                       ssh_buffer buffer,
+                       int reply);
 
 #endif /* CHANNELS_H_ */