- 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

runopts.h

@@ -37,6 +37,7 @@ typedef struct runopts {
 	int listen_fwd_all;
 #endif
 	unsigned int recv_window;
+	time_t keepalive_secs;
 
 } runopts;