- Add -K keepalive flag for dropbear and dbclient

- Try to reduce the frequency of select() timeouts
- Add a max receive window size of 1MB

--HG--
extra : convert_revision : 9aa22036cb511cddb35fbc0e09ad05acb39b64d1

packet.c

@@ -71,6 +71,8 @@ void write_packet() {
 			dropbear_exit("error writing");
 		}
 	} 
+	
+	ses.last_packet_time = time(NULL);
 
 	if (written == 0) {
 		ses.remoteclosed();