Fix issue with TS-570S|D open in rig_caps

If the ts570 backend was called without the radio being turned on or the
wrong IO port specified, the library would generate a number of timeouts
and then fall through to behaving as though the communications channel
were opened.  Discovered that the backend did not specify a function for
rig_open in the rig_caps structure.

Thanks to Volker Schroer, DL1KSV, for reporting this issue.

kenwood/ts570.c

@@ -805,6 +805,7 @@ const struct rig_caps ts570s_caps = {
 .priv =  (void *)&ts570_priv_caps,
 
 .rig_init = kenwood_init,
+.rig_open = kenwood_open,
 .rig_cleanup = kenwood_cleanup,
 .set_freq =  kenwood_set_freq,
 .get_freq =  kenwood_get_freq,
@@ -989,6 +990,7 @@ const struct rig_caps ts570d_caps = {
 .priv =  (void *)&ts570_priv_caps,
 
 .rig_init = kenwood_init,
+.rig_open = kenwood_open,
 .rig_cleanup = kenwood_cleanup,
 .set_freq =  kenwood_set_freq,
 .get_freq =  kenwood_get_freq,